Abstract β-Galactosidases from seven plants have been extensively purified by affinity chromatogr... more Abstract β-Galactosidases from seven plants have been extensively purified by affinity chromatography of an ammonium sulphate concentrate of the respective extracts through a column of Lactosyl-Sepharose. Five of the enzymes are composed of two subunits ranging in M r from 42 to 45 000 and 31 to 35 000 respectively. A sixth enzyme apparently contains two M r 34 000 subunits and a seventh is a M r 46 000 single-subunit protein. All enzymes show charge heterogeneity containing from two to 11 enzymically active isoelectric forms. A major advantage of the purification method employed is the co-purification of all isoelectric forms of each enzyme.
<jats:p>ΑΝΑΠΤΥΧΘΗΚΕ ΕΝΑ ΣΥΣΤΗΜΑ ΠΡΩΤΕΙΝΟΣΥΝΘΕΣΗΣ ΕΛΕΥΘΕΡΟ ΚΥΤΤΑΡΩΝ ΑΠΟ ΣΥΚΩΤΙ ΠΟΝΤΙΚΩΝC3HB,... more <jats:p>ΑΝΑΠΤΥΧΘΗΚΕ ΕΝΑ ΣΥΣΤΗΜΑ ΠΡΩΤΕΙΝΟΣΥΝΘΕΣΗΣ ΕΛΕΥΘΕΡΟ ΚΥΤΤΑΡΩΝ ΑΠΟ ΣΥΚΩΤΙ ΠΟΝΤΙΚΩΝC3HB, ΜΕ ΚΥΡΙΟ ΧΑΡΑΚΤΗΡΙΣΤΙΚΟ ΤΗΝ ΥΨΗΛΗ ΕΝΔΟΓΕΝΗ ΔΡΑΣΗ. ΑΠΟ ΑΥΤΟΡΑΔΙΟΓΡΑΦΙΑ ΠΡΟΚΥΠΤΕΙ ΟΤΙ, ΜΕ ΤΟ ΕΝΔΟΓΕΝΕΣ MRNA, ΣΥΝΘΕΤΕΤΑΙ ΕΝΑΣ ΜΕΓΑΛΟΣ ΑΡΙΘΜΟΣ ΠΡΟΙΟΝΤΩΝ ΜΕ Μ.Β. ΜΕΓΑΛΥΤΕΡΑ ΤΩΝ 100.000 ΕΩΣ 10.000. ΟΡΙΣΜΕΝΑ ΑΠΟ ΑΥΤΑ ΕΜΦΑΝΙΖΟΝΑΙ ΠΡΩΙΜΑ ΣΤΗ ΚΑΜΠΥΛΗ ΧΡΟΝΟΥ ΕΝΩ ΑΛΛΩΝ Η ΕΜΦΑΝΙΣΗ ΚΑΘΥΣΤΕΡΕΙ. ΠΡΟΣΘΗΚΗ ΚΥΚΛΟΕΞΙΜΙΔΙΟΥ ΔΙΝΕΙ 80% ΑΝΑΣΤΟΛΗ. ΟΙ ΠΡΩΤΕΙΝΕΣ ΠΟΥ ΑΝΑΣΤΕΛΛΟΝΤΑΙ ΚΥΡΙΩΣ ΕΙΝΑΙ ΕΚΕΙΝΕΣ ΠΟΥ ΚΑΘΥΣΤΕΡΟΥΝ ΣΤΗΝ ΚΑΜΠΥΛΗ ΧΡΟΝΟΥ. ΠΡΟΣΘΗΚΗ ΣΠΕΡΜΙΔΙΝΗΣ ΣΕ ΣΥΓΚΕΝΤΡΩΣΕΙΣ 100-500 ΜΜ ΠΡΟΚΑΛΕΙ ΕΝΕΡΓΟΠΟΙΗΣΗ ΕΝΩ ΣΕ ΜΕΓΑΛΥΤΕΡΕΣ ΣΥΓΚΕΝΤΡΩΣΕΙΣ ΠΡΟΚΑΛΕΙ ΑΝΑΣΤΟΛΗ. ΗΣΠΕΡΜΙΝΗ ΠΡΟΚΑΛΕΙ ΜΕΓΑΛΗ ΑΝΑΣΤΟΛΗ. ΠΑΡΟΥΣΙΑ ΤΩΝ ΑΝΑΣΤΑΛΤΙΚΩΝ ΣΥΓΚΕΝΤΡΩΣΕΩΝ ΤΗΣ ΣΠΕΡΜΙΔΙΝΗΣ ΔΥΟ ΠΡΩΤΕΙΝΕΣ ΜΕ Μ.Β 14,5 ΚΑΙ 15,5 KD ΦΑΙΝΕΤΑΙ ΝΑ ΙΣΧΥΡΟΠΟΙΟΥΝΤΑΙ. ΤΟ ΣΥΣΤΗΜΑ ΕΧΕΙ ΤΗΝ ΙΚΑΝΟΤΗΤΑ ΝΑ ΜΕΤΑΦΡΑΖΕΙ ΕΞΩΓΕΝΗ MRNA (MRNA ΣΦΑΙΡΙΝΗΣ, TMV RNA) ΕΙΤΕ ΜΕΤΑ ΑΠΟ ΚΑΤΕΡΓΑΣΙΑ ΜΕ ΜΙΚΡΟΚΟΚΚΙΚΗ ΝΟΥΚΛΕΑΣΗ ΕΙΤΕ ΜΕΤΑ ΑΠΟ ΠΡΟΕΠΩΑΣΗ ΓΙΑ ΤΗΝ ΕΞΑΝΤΛΗΣΗ ΤΟΥ ΕΝΔΟΓΕΝΟΥΣ MRNA. ΣΤΗ ΔΕΥΤΕΡΗ ΠΕΡΙΠΤΩΣΗ ΑΠΑΡΑΙΤΗΤΗ ΕΙΝΑΙ Η ΠΡΟΣΘΗΚΗ ΠΑΡΑΓΟΝΤΩΝ ΕΝΑΡΞΗΣ. ΜΑΖΙ ΜΕ ΤΟΥΣ ΠΑΡΑΓΟΝΤΕΣ ΕΝΑΡΞΗΣ ΕΚΧΥΛΙΖΕΤΑΙ ΚΑΙ ΕΝΑΣ ΑΝΑΣΤΟΛΕΑΣ, ΠΟΥ ΜΕΤΑ ΑΠΟ ΚΑΘΑΡΙΣΜΟ ΣΕ DEAE-BIOGEL A, SEPHADEX G-50, ΚΑΙ BIOGEL P2 ΔΙΑΠΙΣΤΩΘΗΚΕ ΟΤΙ ΠΡΟΚΕΙΤΑΙ ΓΙΑ ΜΙΚΡΑ ΠΟΣΑ ΑΜΙΝΟΞΕΩΝ ΠΟΥ ΑΠΛΩΣ ΑΡΑΙΩΝΟΥΝ ΤΟ ΑΝΤΙΣΤΟΙΧΟ ΡΑΔΙΕΝΕΡΓΟ ΑΜΙΝΟΞΥ.</jats:p>
In common with certain other cellular proteins, a CAAX motif (C=cysteine, A=Aliphatic, X=any amin... more In common with certain other cellular proteins, a CAAX motif (C=cysteine, A=Aliphatic, X=any amino acid) is found at the C-terminus of all ras proteins. This motif undergoes a triplet of closely coupled post-translational modifications. First, a prenoid derivative is linked as a thioether to the cysteine residue (Hancock et al,1989; Casey et al,1989), second, the -AAX amino acids are removed by proteolysis (Gutierriez et al,1989) and third, the α-carboxyl group of the now C-terminal cysteine residue is methyl-esterified (Clarke et al,1988; Gutierrez et al,1989). Although the p21ras proteins, the nuclear lamins A and B and the γ-subunit of transducin (Fukada et al, 1990: Lai et al, 1990) are all prenylated with C15 farnesyl, prenylation of proteins with C20 geranylgeranyl is some 10x more common than farnesylation (Epstein et al, 1990). Recently, certain CAAX containing proteins have been identified which are geranylgeranylated, these include the γ-subunits of brain G-proteins (Yamane et al,1990; Mumby et al,1990) and the ras-related proteins Krev1/rap1A (Kawata et al,1990; Buss et al,1991) and G25K (Maltese and Sheridan, 1990). A common feature of the CAAX motifs of these C20 modified proteins is the presence of a leucine residue in the X position. This raises the possibility that the X amino acid determines which isoprenoid residue is used to prenylate a CAAX motif. In addition to the prenylation of CAAX boxes, it is likely that the ras-related rab proteins, which terminate in CC or CXC motifs, might also undergo prenylation since it is known that for these proteins the C-terminal cysteines are essential for function.
SR Protein Kinases (SRPKs), discovered approximately 30 years ago, are widely known as splice fac... more SR Protein Kinases (SRPKs), discovered approximately 30 years ago, are widely known as splice factor kinases due to their decisive involvement in the regulation of various steps of mRNA splicing. However, they were also shown to regulate diverse cellular activities by phosphorylation of serine residues residing in serine-arginine/arginine-serine dipeptide motifs. Over the last decade, SRPK1 has been reported as both tumor suppressor and promoter, depending on the cellular context and has been implicated in both chemotherapy sensitivity and resistance. Moreover, SRPK2 has been reported to exhibit contradictory functions in different cell contexts promoting either apoptosis or tumor growth. The aim of the current review is to broaden and deepen our understanding of the SRPK function focusing on the subcellular localization of the kinases. There is ample evidence that the balance between cytoplasmic and nuclear SRPK levels is tightly regulated and determines cell response to external s...
Chemotherapeutic agents are frequently used to treat various cancers, but the mechanisms mediatin... more Chemotherapeutic agents are frequently used to treat various cancers, but the mechanisms mediating the cellular response to the drugs are still not fully understood. We previously reported that the nuclear translocation of serine/arginine protein kinases (SRPKs), triggered by the exposure of cells to DNA damage-inducers, plays a pivotal role in drug responsiveness. Here, we investigated the mechanism linking the nuclear accumulation of SRPK2 to the cisplatin treatment of HeLa cells. We present experimental evidence that nuclear SRPK2 acts downstream of Chk2 in the ATM/Chk2 cascade. The inhibition of ATM or Chk2 kinase activity by specific low-molecular-weight inhibitors restricted SRPK2 to the cytoplasm and conferred tolerance to cisplatin treatment. A similar effect was achieved by treating cells with SRPIN340, a selective SRPK1/2 inhibitor, thus confirming previous findings that kinase activity is indispensable for the nuclear import of SRPKs. These data add to previous findings t...
<jats:p>ΑΝΑΠΤΥΧΘΗΚΕ ΕΝΑ ΣΥΣΤΗΜΑ ΠΡΩΤΕΙΝΟΣΥΝΘΕΣΗΣ ΕΛΕΥΘΕΡΟ ΚΥΤΤΑΡΩΝ ΑΠΟ ΣΥΚΩΤΙ ΠΟΝΤΙΚΩΝC3HB,... more <jats:p>ΑΝΑΠΤΥΧΘΗΚΕ ΕΝΑ ΣΥΣΤΗΜΑ ΠΡΩΤΕΙΝΟΣΥΝΘΕΣΗΣ ΕΛΕΥΘΕΡΟ ΚΥΤΤΑΡΩΝ ΑΠΟ ΣΥΚΩΤΙ ΠΟΝΤΙΚΩΝC3HB, ΜΕ ΚΥΡΙΟ ΧΑΡΑΚΤΗΡΙΣΤΙΚΟ ΤΗΝ ΥΨΗΛΗ ΕΝΔΟΓΕΝΗ ΔΡΑΣΗ. ΑΠΟ ΑΥΤΟΡΑΔΙΟΓΡΑΦΙΑ ΠΡΟΚΥΠΤΕΙ ΟΤΙ, ΜΕ ΤΟ ΕΝΔΟΓΕΝΕΣ MRNA, ΣΥΝΘΕΤΕΤΑΙ ΕΝΑΣ ΜΕΓΑΛΟΣ ΑΡΙΘΜΟΣ ΠΡΟΙΟΝΤΩΝ ΜΕ Μ.Β. ΜΕΓΑΛΥΤΕΡΑ ΤΩΝ 100.000 ΕΩΣ 10.000. ΟΡΙΣΜΕΝΑ ΑΠΟ ΑΥΤΑ ΕΜΦΑΝΙΖΟΝΑΙ ΠΡΩΙΜΑ ΣΤΗ ΚΑΜΠΥΛΗ ΧΡΟΝΟΥ ΕΝΩ ΑΛΛΩΝ Η ΕΜΦΑΝΙΣΗ ΚΑΘΥΣΤΕΡΕΙ. ΠΡΟΣΘΗΚΗ ΚΥΚΛΟΕΞΙΜΙΔΙΟΥ ΔΙΝΕΙ 80% ΑΝΑΣΤΟΛΗ. ΟΙ ΠΡΩΤΕΙΝΕΣ ΠΟΥ ΑΝΑΣΤΕΛΛΟΝΤΑΙ ΚΥΡΙΩΣ ΕΙΝΑΙ ΕΚΕΙΝΕΣ ΠΟΥ ΚΑΘΥΣΤΕΡΟΥΝ ΣΤΗΝ ΚΑΜΠΥΛΗ ΧΡΟΝΟΥ. ΠΡΟΣΘΗΚΗ ΣΠΕΡΜΙΔΙΝΗΣ ΣΕ ΣΥΓΚΕΝΤΡΩΣΕΙΣ 100-500 ΜΜ ΠΡΟΚΑΛΕΙ ΕΝΕΡΓΟΠΟΙΗΣΗ ΕΝΩ ΣΕ ΜΕΓΑΛΥΤΕΡΕΣ ΣΥΓΚΕΝΤΡΩΣΕΙΣ ΠΡΟΚΑΛΕΙ ΑΝΑΣΤΟΛΗ. ΗΣΠΕΡΜΙΝΗ ΠΡΟΚΑΛΕΙ ΜΕΓΑΛΗ ΑΝΑΣΤΟΛΗ. ΠΑΡΟΥΣΙΑ ΤΩΝ ΑΝΑΣΤΑΛΤΙΚΩΝ ΣΥΓΚΕΝΤΡΩΣΕΩΝ ΤΗΣ ΣΠΕΡΜΙΔΙΝΗΣ ΔΥΟ ΠΡΩΤΕΙΝΕΣ ΜΕ Μ.Β 14,5 ΚΑΙ 15,5 KD ΦΑΙΝΕΤΑΙ ΝΑ ΙΣΧΥΡΟΠΟΙΟΥΝΤΑΙ. ΤΟ ΣΥΣΤΗΜΑ ΕΧΕΙ ΤΗΝ ΙΚΑΝΟΤΗΤΑ ΝΑ ΜΕΤΑΦΡΑΖΕΙ ΕΞΩΓΕΝΗ MRNA (MRNA ΣΦΑΙΡΙΝΗΣ, TMV RNA) ΕΙΤΕ ΜΕΤΑ ΑΠΟ ΚΑΤΕΡΓΑΣΙΑ ΜΕ ΜΙΚΡΟΚΟΚΚΙΚΗ ΝΟΥΚΛΕΑΣΗ ΕΙΤΕ ΜΕΤΑ ΑΠΟ ΠΡΟΕΠΩΑΣΗ ΓΙΑ ΤΗΝ ΕΞΑΝΤΛΗΣΗ ΤΟΥ ΕΝΔΟΓΕΝΟΥΣ MRNA. ΣΤΗ ΔΕΥΤΕΡΗ ΠΕΡΙΠΤΩΣΗ ΑΠΑΡΑΙΤΗΤΗ ΕΙΝΑΙ Η ΠΡΟΣΘΗΚΗ ΠΑΡΑΓΟΝΤΩΝ ΕΝΑΡΞΗΣ. ΜΑΖΙ ΜΕ ΤΟΥΣ ΠΑΡΑΓΟΝΤΕΣ ΕΝΑΡΞΗΣ ΕΚΧΥΛΙΖΕΤΑΙ ΚΑΙ ΕΝΑΣ ΑΝΑΣΤΟΛΕΑΣ, ΠΟΥ ΜΕΤΑ ΑΠΟ ΚΑΘΑΡΙΣΜΟ ΣΕ DEAE-BIOGEL A, SEPHADEX G-50, ΚΑΙ BIOGEL P2 ΔΙΑΠΙΣΤΩΘΗΚΕ ΟΤΙ ΠΡΟΚΕΙΤΑΙ ΓΙΑ ΜΙΚΡΑ ΠΟΣΑ ΑΜΙΝΟΞΕΩΝ ΠΟΥ ΑΠΛΩΣ ΑΡΑΙΩΝΟΥΝ ΤΟ ΑΝΤΙΣΤΟΙΧΟ ΡΑΔΙΕΝΕΡΓΟ ΑΜΙΝΟΞΥ.</jats:p>
Over the last 12 years or so, a group of posttranslational modifications of proteins with various... more Over the last 12 years or so, a group of posttranslational modifications of proteins with various lipid molecules has been identified in eukaryotic cells (for reviews see Schmidt 1989; McIlhinney 1990; Gordon et al. 1991; Magee 1991). In many cases these modifications have been shown to be essential for the subcellular localization of the proteins carrying them. Many intracellular proteins are now known to carry fatty acid modifications which serve such a purpose. The 14 carbon saturated fatty acid myris-tate (C14:0) is amide-linked to the NH2-terminal of a range of proteins, exemplified by the pp60src proto-oncogene product. Site-directed mutagenesis has been used to demonstrate that this acylation is required both for membrane localization and transforming activity. The myristoylation enzyme has been isolated and is highly specific for acyl chain length. Inhibitors which interfere with this pathway provide an attractive approach to specific chemotherapies of cancers and viral infections including HIV.
Acetyl-coenzyme A (CoASAc) inhibits the rate of incorporation of amino acid into protein in a cel... more Acetyl-coenzyme A (CoASAc) inhibits the rate of incorporation of amino acid into protein in a cell-free system of mouse liver. The effect is more pronounced when exogenous mRNA (tobacco mosaic virus or globin mRNA) rather than endogenous messages are used. Micromolar concentrations of the cofactor block initiation, while millimolar concentrations cause a more general inhibition of the translation process, that affects, in addition, the elongation step. Inclusion of [1-14C]acetyl-CoA in a protein synthesis reaction mixture results in a very rapid and selective labelling of a protein of 200 kd of the 'pH 5' fraction. The possible involvement of the acetylating event in the regulation of protein synthesis is discussed.
Abstract β-Galactosidases from seven plants have been extensively purified by affinity chromatogr... more Abstract β-Galactosidases from seven plants have been extensively purified by affinity chromatography of an ammonium sulphate concentrate of the respective extracts through a column of Lactosyl-Sepharose. Five of the enzymes are composed of two subunits ranging in M r from 42 to 45 000 and 31 to 35 000 respectively. A sixth enzyme apparently contains two M r 34 000 subunits and a seventh is a M r 46 000 single-subunit protein. All enzymes show charge heterogeneity containing from two to 11 enzymically active isoelectric forms. A major advantage of the purification method employed is the co-purification of all isoelectric forms of each enzyme.
<jats:p>ΑΝΑΠΤΥΧΘΗΚΕ ΕΝΑ ΣΥΣΤΗΜΑ ΠΡΩΤΕΙΝΟΣΥΝΘΕΣΗΣ ΕΛΕΥΘΕΡΟ ΚΥΤΤΑΡΩΝ ΑΠΟ ΣΥΚΩΤΙ ΠΟΝΤΙΚΩΝC3HB,... more <jats:p>ΑΝΑΠΤΥΧΘΗΚΕ ΕΝΑ ΣΥΣΤΗΜΑ ΠΡΩΤΕΙΝΟΣΥΝΘΕΣΗΣ ΕΛΕΥΘΕΡΟ ΚΥΤΤΑΡΩΝ ΑΠΟ ΣΥΚΩΤΙ ΠΟΝΤΙΚΩΝC3HB, ΜΕ ΚΥΡΙΟ ΧΑΡΑΚΤΗΡΙΣΤΙΚΟ ΤΗΝ ΥΨΗΛΗ ΕΝΔΟΓΕΝΗ ΔΡΑΣΗ. ΑΠΟ ΑΥΤΟΡΑΔΙΟΓΡΑΦΙΑ ΠΡΟΚΥΠΤΕΙ ΟΤΙ, ΜΕ ΤΟ ΕΝΔΟΓΕΝΕΣ MRNA, ΣΥΝΘΕΤΕΤΑΙ ΕΝΑΣ ΜΕΓΑΛΟΣ ΑΡΙΘΜΟΣ ΠΡΟΙΟΝΤΩΝ ΜΕ Μ.Β. ΜΕΓΑΛΥΤΕΡΑ ΤΩΝ 100.000 ΕΩΣ 10.000. ΟΡΙΣΜΕΝΑ ΑΠΟ ΑΥΤΑ ΕΜΦΑΝΙΖΟΝΑΙ ΠΡΩΙΜΑ ΣΤΗ ΚΑΜΠΥΛΗ ΧΡΟΝΟΥ ΕΝΩ ΑΛΛΩΝ Η ΕΜΦΑΝΙΣΗ ΚΑΘΥΣΤΕΡΕΙ. ΠΡΟΣΘΗΚΗ ΚΥΚΛΟΕΞΙΜΙΔΙΟΥ ΔΙΝΕΙ 80% ΑΝΑΣΤΟΛΗ. ΟΙ ΠΡΩΤΕΙΝΕΣ ΠΟΥ ΑΝΑΣΤΕΛΛΟΝΤΑΙ ΚΥΡΙΩΣ ΕΙΝΑΙ ΕΚΕΙΝΕΣ ΠΟΥ ΚΑΘΥΣΤΕΡΟΥΝ ΣΤΗΝ ΚΑΜΠΥΛΗ ΧΡΟΝΟΥ. ΠΡΟΣΘΗΚΗ ΣΠΕΡΜΙΔΙΝΗΣ ΣΕ ΣΥΓΚΕΝΤΡΩΣΕΙΣ 100-500 ΜΜ ΠΡΟΚΑΛΕΙ ΕΝΕΡΓΟΠΟΙΗΣΗ ΕΝΩ ΣΕ ΜΕΓΑΛΥΤΕΡΕΣ ΣΥΓΚΕΝΤΡΩΣΕΙΣ ΠΡΟΚΑΛΕΙ ΑΝΑΣΤΟΛΗ. ΗΣΠΕΡΜΙΝΗ ΠΡΟΚΑΛΕΙ ΜΕΓΑΛΗ ΑΝΑΣΤΟΛΗ. ΠΑΡΟΥΣΙΑ ΤΩΝ ΑΝΑΣΤΑΛΤΙΚΩΝ ΣΥΓΚΕΝΤΡΩΣΕΩΝ ΤΗΣ ΣΠΕΡΜΙΔΙΝΗΣ ΔΥΟ ΠΡΩΤΕΙΝΕΣ ΜΕ Μ.Β 14,5 ΚΑΙ 15,5 KD ΦΑΙΝΕΤΑΙ ΝΑ ΙΣΧΥΡΟΠΟΙΟΥΝΤΑΙ. ΤΟ ΣΥΣΤΗΜΑ ΕΧΕΙ ΤΗΝ ΙΚΑΝΟΤΗΤΑ ΝΑ ΜΕΤΑΦΡΑΖΕΙ ΕΞΩΓΕΝΗ MRNA (MRNA ΣΦΑΙΡΙΝΗΣ, TMV RNA) ΕΙΤΕ ΜΕΤΑ ΑΠΟ ΚΑΤΕΡΓΑΣΙΑ ΜΕ ΜΙΚΡΟΚΟΚΚΙΚΗ ΝΟΥΚΛΕΑΣΗ ΕΙΤΕ ΜΕΤΑ ΑΠΟ ΠΡΟΕΠΩΑΣΗ ΓΙΑ ΤΗΝ ΕΞΑΝΤΛΗΣΗ ΤΟΥ ΕΝΔΟΓΕΝΟΥΣ MRNA. ΣΤΗ ΔΕΥΤΕΡΗ ΠΕΡΙΠΤΩΣΗ ΑΠΑΡΑΙΤΗΤΗ ΕΙΝΑΙ Η ΠΡΟΣΘΗΚΗ ΠΑΡΑΓΟΝΤΩΝ ΕΝΑΡΞΗΣ. ΜΑΖΙ ΜΕ ΤΟΥΣ ΠΑΡΑΓΟΝΤΕΣ ΕΝΑΡΞΗΣ ΕΚΧΥΛΙΖΕΤΑΙ ΚΑΙ ΕΝΑΣ ΑΝΑΣΤΟΛΕΑΣ, ΠΟΥ ΜΕΤΑ ΑΠΟ ΚΑΘΑΡΙΣΜΟ ΣΕ DEAE-BIOGEL A, SEPHADEX G-50, ΚΑΙ BIOGEL P2 ΔΙΑΠΙΣΤΩΘΗΚΕ ΟΤΙ ΠΡΟΚΕΙΤΑΙ ΓΙΑ ΜΙΚΡΑ ΠΟΣΑ ΑΜΙΝΟΞΕΩΝ ΠΟΥ ΑΠΛΩΣ ΑΡΑΙΩΝΟΥΝ ΤΟ ΑΝΤΙΣΤΟΙΧΟ ΡΑΔΙΕΝΕΡΓΟ ΑΜΙΝΟΞΥ.</jats:p>
In common with certain other cellular proteins, a CAAX motif (C=cysteine, A=Aliphatic, X=any amin... more In common with certain other cellular proteins, a CAAX motif (C=cysteine, A=Aliphatic, X=any amino acid) is found at the C-terminus of all ras proteins. This motif undergoes a triplet of closely coupled post-translational modifications. First, a prenoid derivative is linked as a thioether to the cysteine residue (Hancock et al,1989; Casey et al,1989), second, the -AAX amino acids are removed by proteolysis (Gutierriez et al,1989) and third, the α-carboxyl group of the now C-terminal cysteine residue is methyl-esterified (Clarke et al,1988; Gutierrez et al,1989). Although the p21ras proteins, the nuclear lamins A and B and the γ-subunit of transducin (Fukada et al, 1990: Lai et al, 1990) are all prenylated with C15 farnesyl, prenylation of proteins with C20 geranylgeranyl is some 10x more common than farnesylation (Epstein et al, 1990). Recently, certain CAAX containing proteins have been identified which are geranylgeranylated, these include the γ-subunits of brain G-proteins (Yamane et al,1990; Mumby et al,1990) and the ras-related proteins Krev1/rap1A (Kawata et al,1990; Buss et al,1991) and G25K (Maltese and Sheridan, 1990). A common feature of the CAAX motifs of these C20 modified proteins is the presence of a leucine residue in the X position. This raises the possibility that the X amino acid determines which isoprenoid residue is used to prenylate a CAAX motif. In addition to the prenylation of CAAX boxes, it is likely that the ras-related rab proteins, which terminate in CC or CXC motifs, might also undergo prenylation since it is known that for these proteins the C-terminal cysteines are essential for function.
SR Protein Kinases (SRPKs), discovered approximately 30 years ago, are widely known as splice fac... more SR Protein Kinases (SRPKs), discovered approximately 30 years ago, are widely known as splice factor kinases due to their decisive involvement in the regulation of various steps of mRNA splicing. However, they were also shown to regulate diverse cellular activities by phosphorylation of serine residues residing in serine-arginine/arginine-serine dipeptide motifs. Over the last decade, SRPK1 has been reported as both tumor suppressor and promoter, depending on the cellular context and has been implicated in both chemotherapy sensitivity and resistance. Moreover, SRPK2 has been reported to exhibit contradictory functions in different cell contexts promoting either apoptosis or tumor growth. The aim of the current review is to broaden and deepen our understanding of the SRPK function focusing on the subcellular localization of the kinases. There is ample evidence that the balance between cytoplasmic and nuclear SRPK levels is tightly regulated and determines cell response to external s...
Chemotherapeutic agents are frequently used to treat various cancers, but the mechanisms mediatin... more Chemotherapeutic agents are frequently used to treat various cancers, but the mechanisms mediating the cellular response to the drugs are still not fully understood. We previously reported that the nuclear translocation of serine/arginine protein kinases (SRPKs), triggered by the exposure of cells to DNA damage-inducers, plays a pivotal role in drug responsiveness. Here, we investigated the mechanism linking the nuclear accumulation of SRPK2 to the cisplatin treatment of HeLa cells. We present experimental evidence that nuclear SRPK2 acts downstream of Chk2 in the ATM/Chk2 cascade. The inhibition of ATM or Chk2 kinase activity by specific low-molecular-weight inhibitors restricted SRPK2 to the cytoplasm and conferred tolerance to cisplatin treatment. A similar effect was achieved by treating cells with SRPIN340, a selective SRPK1/2 inhibitor, thus confirming previous findings that kinase activity is indispensable for the nuclear import of SRPKs. These data add to previous findings t...
<jats:p>ΑΝΑΠΤΥΧΘΗΚΕ ΕΝΑ ΣΥΣΤΗΜΑ ΠΡΩΤΕΙΝΟΣΥΝΘΕΣΗΣ ΕΛΕΥΘΕΡΟ ΚΥΤΤΑΡΩΝ ΑΠΟ ΣΥΚΩΤΙ ΠΟΝΤΙΚΩΝC3HB,... more <jats:p>ΑΝΑΠΤΥΧΘΗΚΕ ΕΝΑ ΣΥΣΤΗΜΑ ΠΡΩΤΕΙΝΟΣΥΝΘΕΣΗΣ ΕΛΕΥΘΕΡΟ ΚΥΤΤΑΡΩΝ ΑΠΟ ΣΥΚΩΤΙ ΠΟΝΤΙΚΩΝC3HB, ΜΕ ΚΥΡΙΟ ΧΑΡΑΚΤΗΡΙΣΤΙΚΟ ΤΗΝ ΥΨΗΛΗ ΕΝΔΟΓΕΝΗ ΔΡΑΣΗ. ΑΠΟ ΑΥΤΟΡΑΔΙΟΓΡΑΦΙΑ ΠΡΟΚΥΠΤΕΙ ΟΤΙ, ΜΕ ΤΟ ΕΝΔΟΓΕΝΕΣ MRNA, ΣΥΝΘΕΤΕΤΑΙ ΕΝΑΣ ΜΕΓΑΛΟΣ ΑΡΙΘΜΟΣ ΠΡΟΙΟΝΤΩΝ ΜΕ Μ.Β. ΜΕΓΑΛΥΤΕΡΑ ΤΩΝ 100.000 ΕΩΣ 10.000. ΟΡΙΣΜΕΝΑ ΑΠΟ ΑΥΤΑ ΕΜΦΑΝΙΖΟΝΑΙ ΠΡΩΙΜΑ ΣΤΗ ΚΑΜΠΥΛΗ ΧΡΟΝΟΥ ΕΝΩ ΑΛΛΩΝ Η ΕΜΦΑΝΙΣΗ ΚΑΘΥΣΤΕΡΕΙ. ΠΡΟΣΘΗΚΗ ΚΥΚΛΟΕΞΙΜΙΔΙΟΥ ΔΙΝΕΙ 80% ΑΝΑΣΤΟΛΗ. ΟΙ ΠΡΩΤΕΙΝΕΣ ΠΟΥ ΑΝΑΣΤΕΛΛΟΝΤΑΙ ΚΥΡΙΩΣ ΕΙΝΑΙ ΕΚΕΙΝΕΣ ΠΟΥ ΚΑΘΥΣΤΕΡΟΥΝ ΣΤΗΝ ΚΑΜΠΥΛΗ ΧΡΟΝΟΥ. ΠΡΟΣΘΗΚΗ ΣΠΕΡΜΙΔΙΝΗΣ ΣΕ ΣΥΓΚΕΝΤΡΩΣΕΙΣ 100-500 ΜΜ ΠΡΟΚΑΛΕΙ ΕΝΕΡΓΟΠΟΙΗΣΗ ΕΝΩ ΣΕ ΜΕΓΑΛΥΤΕΡΕΣ ΣΥΓΚΕΝΤΡΩΣΕΙΣ ΠΡΟΚΑΛΕΙ ΑΝΑΣΤΟΛΗ. ΗΣΠΕΡΜΙΝΗ ΠΡΟΚΑΛΕΙ ΜΕΓΑΛΗ ΑΝΑΣΤΟΛΗ. ΠΑΡΟΥΣΙΑ ΤΩΝ ΑΝΑΣΤΑΛΤΙΚΩΝ ΣΥΓΚΕΝΤΡΩΣΕΩΝ ΤΗΣ ΣΠΕΡΜΙΔΙΝΗΣ ΔΥΟ ΠΡΩΤΕΙΝΕΣ ΜΕ Μ.Β 14,5 ΚΑΙ 15,5 KD ΦΑΙΝΕΤΑΙ ΝΑ ΙΣΧΥΡΟΠΟΙΟΥΝΤΑΙ. ΤΟ ΣΥΣΤΗΜΑ ΕΧΕΙ ΤΗΝ ΙΚΑΝΟΤΗΤΑ ΝΑ ΜΕΤΑΦΡΑΖΕΙ ΕΞΩΓΕΝΗ MRNA (MRNA ΣΦΑΙΡΙΝΗΣ, TMV RNA) ΕΙΤΕ ΜΕΤΑ ΑΠΟ ΚΑΤΕΡΓΑΣΙΑ ΜΕ ΜΙΚΡΟΚΟΚΚΙΚΗ ΝΟΥΚΛΕΑΣΗ ΕΙΤΕ ΜΕΤΑ ΑΠΟ ΠΡΟΕΠΩΑΣΗ ΓΙΑ ΤΗΝ ΕΞΑΝΤΛΗΣΗ ΤΟΥ ΕΝΔΟΓΕΝΟΥΣ MRNA. ΣΤΗ ΔΕΥΤΕΡΗ ΠΕΡΙΠΤΩΣΗ ΑΠΑΡΑΙΤΗΤΗ ΕΙΝΑΙ Η ΠΡΟΣΘΗΚΗ ΠΑΡΑΓΟΝΤΩΝ ΕΝΑΡΞΗΣ. ΜΑΖΙ ΜΕ ΤΟΥΣ ΠΑΡΑΓΟΝΤΕΣ ΕΝΑΡΞΗΣ ΕΚΧΥΛΙΖΕΤΑΙ ΚΑΙ ΕΝΑΣ ΑΝΑΣΤΟΛΕΑΣ, ΠΟΥ ΜΕΤΑ ΑΠΟ ΚΑΘΑΡΙΣΜΟ ΣΕ DEAE-BIOGEL A, SEPHADEX G-50, ΚΑΙ BIOGEL P2 ΔΙΑΠΙΣΤΩΘΗΚΕ ΟΤΙ ΠΡΟΚΕΙΤΑΙ ΓΙΑ ΜΙΚΡΑ ΠΟΣΑ ΑΜΙΝΟΞΕΩΝ ΠΟΥ ΑΠΛΩΣ ΑΡΑΙΩΝΟΥΝ ΤΟ ΑΝΤΙΣΤΟΙΧΟ ΡΑΔΙΕΝΕΡΓΟ ΑΜΙΝΟΞΥ.</jats:p>
Over the last 12 years or so, a group of posttranslational modifications of proteins with various... more Over the last 12 years or so, a group of posttranslational modifications of proteins with various lipid molecules has been identified in eukaryotic cells (for reviews see Schmidt 1989; McIlhinney 1990; Gordon et al. 1991; Magee 1991). In many cases these modifications have been shown to be essential for the subcellular localization of the proteins carrying them. Many intracellular proteins are now known to carry fatty acid modifications which serve such a purpose. The 14 carbon saturated fatty acid myris-tate (C14:0) is amide-linked to the NH2-terminal of a range of proteins, exemplified by the pp60src proto-oncogene product. Site-directed mutagenesis has been used to demonstrate that this acylation is required both for membrane localization and transforming activity. The myristoylation enzyme has been isolated and is highly specific for acyl chain length. Inhibitors which interfere with this pathway provide an attractive approach to specific chemotherapies of cancers and viral infections including HIV.
Acetyl-coenzyme A (CoASAc) inhibits the rate of incorporation of amino acid into protein in a cel... more Acetyl-coenzyme A (CoASAc) inhibits the rate of incorporation of amino acid into protein in a cell-free system of mouse liver. The effect is more pronounced when exogenous mRNA (tobacco mosaic virus or globin mRNA) rather than endogenous messages are used. Micromolar concentrations of the cofactor block initiation, while millimolar concentrations cause a more general inhibition of the translation process, that affects, in addition, the elongation step. Inclusion of [1-14C]acetyl-CoA in a protein synthesis reaction mixture results in a very rapid and selective labelling of a protein of 200 kd of the 'pH 5' fraction. The possible involvement of the acetylating event in the regulation of protein synthesis is discussed.
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