Alternate Pathways of Bacteriophage M 13 DNA Replication

Novel replicative properties of a capsid mutant of bacteriophage phi chi 174

“…We observed previously that kXahb exhibits 6 x certain synthetic capacities more characteristic w I of bacteriophage M13 than of 4X174, e.g., abil-^1 20 ity to form parental RF DNA in a thermosensi-[ tive dnaB mutant of E. coli (5,28,33). There-4 fore, we tested the possibility that, although fXahb parental RF DNA formation is rifampin-resistant in wild-type cells (Fig.…”

“…Symbols: A, '4C-labeled SS 4X174 viral DNA marker; *, 32P-labeled input 4Xahb. Recently, it was shown that a rifampinsensitive mechanism is involved in the conver- 30 Z. sion of M13 single-stranded viral DNA to dou-e t ble-stranded parental RF DNA in E. coli (28).…”

“…At least two distinct replicative systems have been resolved with respect to the small, singlestranded DNA phages; one is representative of the mechanism by which M13 replicates (7,15,22), and the other is representative of the mechanism by which 4X174 replicates (22,23,32,35,36). There are three instances in which the differences between these replicative mechanisms are most striking: (i and ii) M13 parental RF DNA formation occurs in the absence of functional dnaB (28) and dnaG (21) protein, whereas that of 4X174 is very much dependent upon the dnaB (5,26,29,33) and CAPSID MUTANT OF OX174 947 the dnaG (14) proteins; (iii) the conversion of M13 viral DNA to parental RF DNA is sensitive to rifampin (22,28,34), whereas that of OX174 is resistant (22,24,25). Knowing that (Xahb differs from 4X174 in that (i) it forms parental RF DNA in the presence of puromycin at 42 C in E. coli C and (ii) it forms parental RF DNA and progeny viral DNA in the absence of functional dnaB (33) and dnaG protein, respectively, we thought it possible that the 4)Xahb mutations allow it to utilize the host replicative apparatus (4) ordinarily involved in M13 DNA synthesis.…”