Miller S D, Crouch E A, Busbee D L
Department of Anatomy and Public Health, College of Veterinary Medicine, Texas A & M University, College Station 77843, USA.
Mutat Res. 1997 Mar 4;374(1):125-38. doi: 10.1016/s0027-5107(96)00232-1.
Isoforms of DNA polymerase alpha (pol alpha/primase; pol alpha) were isolated from the livers of C57BL/6 mice either 3 months old (young) or 13 months old (mature). The 13-month-old mice were from two groups, one in which food was available ad libitum (AL), and one in which calories had been restricted to 60% of the AL intake (CR). The polymerases from young vs. mature and CR vs. AL mice differed in total and specific pol alpha activity, with the highest values exhibited by enzymes from 3-month-old mice. A more active isoform of pol alpha was typically isolated from CR animals than from AL animals. Differences in charge were used to chromatographically separate pol alpha into elution peaks exhibiting differing degrees of enzyme activity. DNA pol alpha isolated from tissues of mature mice exhibited a decline in activity which was not associated with decreased recoverable levels of pol alpha protein, but with a decline in the tendency of pol alpha to co-purify with an accessory protein, alpha AP, that binds double-stranded DNA (dsDNA). Low activity pol alpha isoforms which did not co-purify with alpha AP were stimulated by interaction with exogenous alpha AP. Pol alpha isoforms which co-purified with the dsDNA-binding accessory protein exhibited higher specific activity and less enhancement of activity upon interaction with exogenous alpha AP. Calorie restricted animals exhibited a pol alpha isoform that was more like pol alpha from younger animals in that it typically copurified with alpha AP, the DNA-binding accessory protein.
从3月龄（年轻）或13月龄（成熟）的C57BL/6小鼠肝脏中分离出DNA聚合酶α（pol α/引发酶；pol α）的同工型。13月龄的小鼠分为两组，一组自由摄食（AL），另一组热量摄入限制为AL组摄入量的60%（CR）。年轻小鼠与成熟小鼠以及CR组小鼠与AL组小鼠的聚合酶在总pol α活性和比活性上存在差异，3月龄小鼠的酶活性最高。通常从CR组动物中分离出的pol α同工型比AL组动物的更具活性。利用电荷差异通过色谱法将pol α分离成具有不同酶活性程度的洗脱峰。从成熟小鼠组织中分离出的DNA pol α活性下降，这与pol α蛋白可回收水平的降低无关，而是与pol α与一种结合双链DNA（dsDNA）的辅助蛋白α AP共纯化的趋势下降有关。未与α AP共纯化的低活性pol α同工型通过与外源性α AP相互作用而受到刺激。与dsDNA结合辅助蛋白共纯化的pol α同工型表现出更高的比活性，并且与外源性α AP相互作用时活性增强较少。热量限制的动物表现出一种pol α同工型，它更类似于年轻动物的pol α，因为它通常与DNA结合辅助蛋白α AP共纯化。
