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A M Holmes

Publications and source records attributed to A M Holmes.

9 recordsLinked to original sources
PubMed1979

Further studies on partially purified calf thymus DNA polymerase a.

Attempts to prevent the urea conversion of a 200-230,000 molecular weight DNA polymerase alpha to a 150-170,000 molecular weight form by the inclusion of protease inhibitors have not been successful. No other method has been found capable of dissociating a 50-70,000 fragment or subunit from the DNA polymerase subunit. Addition of this 50-70,000 subunit to the polymerase subunit does not aid the binding of the enzyme to DNA, but does have an effect on the utilisation of synthetic template-initiator complexes by the polymerase subunit.

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PubMed1978

Studies on the purification and properties of a 6.8-S DNA polymerase activity found in calf-thymus DNA polymerase-alpha fraction.

The heterogeneity of calf thymus DNA polymerase-alpha has been further investigated. In particular, an enzyme (enzyme D) which exhibits higher activity on poly(dA) . (dT)10 (A:T = 20:1) compared with that on activated DNA, has been further purified and its properties compared with two other activities of the DNA polymerase-alpha fraction (enzymes A1 and C) which do not show a preference for poly(dA) . (dT)10 over activated DNA. As with A1 and C, enzyme D was shown to have many of the characteristic properties of DNA polymerase-alpha in that it is an acidic protein as judged by its binding to DEAE-cellulose, has a molecular weight of about 140000, does not use a poly (A) . (dT)10 template-initiator complex and is inhibited by N-ethylmaleimide. It exhibits anomalous gel filtration behaviour on Sepharose 6B and it binds relatively weakly to DNA-cellulose compared with DNA polymerase-beta. The extreme sensitivity of enzyme D to inhibtion by N-ethylmaleimide distinguishes it from A1 and C, as does its elution position from a DEAE-cellulose column. On the other hand enzymes C and D are readily inactivated by heating at 45 degrees C unlike enzyme A1. The possible interrelationships of the multiple activities of calf thymus DNA polymerase-alpha are discussed.

Animals↗
PubMed1976

Evidence that DNA polymerase-alpha of calf thymus contains a subunit of molecular weight 155000.

Small samples of the 8-S species of enzymes (A1 and A2) occurring in the DNA polymerase-alpha fraction of calf thymus, have been extensively purified using non-denaturing (normal) polyacrylamide gel electrophoresis. When peak fractions of activity on normal gels were subjected to dodecylsulphate-polyacrylamide gel electrophoresis, a polypeptide at 155000 correlated with polymerase activity. Samples of the 7.3-S (C) enzyme prepared from A2 by treatment with 2.4 M urea or isolated directly without exposure to urea, also showed the presence of a 155000-Mr polypeptide. It is concluded that the 7.3-S (C) enzyme, of previously estimated molecular weight 155000-170000, is a single polypeptide and that the 8-S enzymes A1 and A2 contain an additional subunit of 50000-70000 molecular weight.

Animals↗