Properties of single-stranded DNA-binding proteins (SSB-proteins) from chromatin and nonchromatin fractions of Ehrlich ascites tumour: phosphorylation enhances the affinity of SSB-proteins for single-stranded DNA.
To assess the possible functional role of single-strand DNA-binding (SSB) proteins in eucaryotic cell, a comparative study was made of SSB-proteins isolated from chromatin and the nonchromatin fractions of Ehrlich ascites tumour (EAT) cells. No appreciable differences between the two groups could be found either in SDS-gel electrophoretic patterns or in the ssDNA-binding capacity and stimulation of DNA replication in permeable EAT cells. However, the chromatin SSB-proteins incorporated 1.4-times more labelled phosphate in vivo; phosphate assays in the isolated chromatin and nonchromatin SSB-proteins yielded ca. 3 and 2 moles Pi/mole protein, respectively. Both preparations could be further phosphorylated in vitro with Ca-phospholipid-dependent protein kinase and the catalytic subunit of cAMP-dependent protein kinase, but the non-chromatin proteins were phosphorylated to a greater degree. In parallel with phosphorylation, the SSB-proteins displayed stronger binding to ssDNA cellulose. Phosphorylation may thus be a means of regulating the functions of SSB-proteins, in particular their interaction with chromatin.
Koterov
A N
AN
Institute of Biophysics, USSR Ministry of Health, Moscow.
Novoradovskaja
N A
NA
Nikol'skii
A V
AV
Pushkareva
N B
NB
Vorotnikov
A V
AV
Risnik
V V
VV
D000818:Animals; D002286:Carcinoma, Ehrlich Tumor / Q000737:chemistry* / Q000235:genetics; D002458:Cell Fractionation; D002843:Chromatin / Q000737:chemistry* / Q000201:enzymology; D004277:DNA, Single-Stranded / Q000737:chemistry*; D004268:DNA-Binding Proteins / Q000737:chemistry*; D051379:Mice; D009363:Neoplasm Proteins / Q000737:chemistry*; D010766:Phosphorylation; D011485:Protein Binding
D002843:Chromatin; D004277:DNA, Single-Stranded; D004268:DNA-Binding Proteins; D009363:Neoplasm Proteins