Growth and reactivation of single stranded DNA phageϕX174 in E. coli undergoing “thymineless death”

Abstract

The thymine requirement of the E. coli strain HF 4704 (uvr A-, rec A+) is thermosensitive i.e. these cells require for their growth 2 microng thymine per ml at 37 degrees C but not at 30 degrees C. Such cells when starved for thymine for 3 h at 37 degrees C are capable of sustaining growth of single stranded DNA phage phiX174 without any diminution of burst size under nonpermissive conditions. Thymine starved HF 4704 cells also reactivate UV-irradiated phiX174 by about 3fold. To test if the thymine necessary for phage growth under "thymineless" conditions was supplied by host DNA degradation products, the transfer of 32P label from the host DNA to mature progeny phages was measured by means of sucrose density gradient analysis. It was found that only about 0.7% of 32P of the host DNA was transferred to the progeny phages growing in normal cells whereas the corresponding value was 7.8% in the case of thymine starved cells.

Sources of thymidine and analogs fueling futile damage-repair cycles and ss-gap accumulation during thymine starvation in Escherichia coli

“…2H). In support of the chromosomal DNA instability during Tstarvation, during a phage infection of T-starved cells, there is appreciable incorporation of the chromosomal DNA material in the phage genome, which is not observed in the nonstarved cells (Thakur and Poddar 1977). The potential for intrachromosomal cannibalism is further bolstered by the appearance in response to T-starvation of short-lived relatively small subchromosomal fragments (Fig.…”