A major single-stranded DNA binding protein from ovaries of the frog, Xenopus laevis, is lactate dehydrogenase.
The most abundant single-stranded DNA binding protein (SSB) found in ovaries of the frog, Xenopus laevis, was purified to electrophoretic homogeneity. Under physiological conditions, the purified SSB lowered the Tm of poly[d(A-T)] and stimulated DNA synthesis by the homologous DNA polymerase DNA primase alpha complex on single-stranded DNA templates. These properties are characteristic of a bona fide single-stranded DNA binding protein. The Stokes radius of native SSB was calculated to be 45 A, corresponding to a molecular mass of about 140 kDa. On SDS polyacrylamide gels, the SSB migrated as a single band with a molecular mass of 36 kDa. We assumed, therefore, that the SSB was a tetramer of 36 kDa subunits. We subsequently discovered that the SSB was LDH, D-lactate dehydrogenase, EC 1.1.1.28. Purified SSB has high LDH specific activity. Following electrophoresis on SDS polyacrylamide gels, the 36 kDa subunits were renatured and exhibited LDH activity. The amino-acid composition of X. laevis SSB/LDH was similar to that of LDH from other species and to other reported single-stranded DNA binding proteins. Mammalian SSB/LDH also preferentially bound single-stranded DNA. Mammalian SSB/LDH bound to RNA as demonstrated by affinity chromatography on poly(A)-agarose and by its effect on translation of mRNA in vitro.
Kaiserman
H B
HB
Department of Biology, Johns Hopkins University, Baltimore, MD.
Odenwald
W F
WF
Stowers
D J
DJ
Poll
E H
EH
Benbow
R M
RM
D000595:Amino Acid Sequence; D000818:Animals; D002846:Chromatography, Affinity; D004268:DNA-Binding Proteins / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D005260:Female; D007770:L-Lactate Dehydrogenase / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D046911:Macromolecular Substances; D008969:Molecular Sequence Data; D008970:Molecular Weight; D010053:Ovary / Q000201:enzymology*; D012313:RNA / Q000378:metabolism; D013552:Swine; D014982:Xenopus laevis
D004268:DNA-Binding Proteins; D046911:Macromolecular Substances; D012313:RNA; D007770:L-Lactate Dehydrogenase