Suppression of initiation-negative strains of Escherichia coli by integration of the sex factor F

Abstract

Data are presented suggesting that the most critical factor determining whether an Hfr dnaAts strain can synthesize deoxyribonucleic acid and form colonies at temperatures that are nonpermissive for corresponding F- strains is neither the site of insertion of F nor the presence of additional mutations in the F particle or the chromosome; it is whether the particle is capable of autonomous replication at the temperature used. Consequently, suppression of the DnaA phenotype in Hfr strains occurs at 40 C but not, in most of them, at 42 C without the occurrence of additional mutations. The site of insertion of F may also be important since it is shown that in one Hfr dnaA strain partial suppression does occur at 42 C. In addition, it is shown that strains exhibiting suppression by integration of F at 40 C on minimal agar plates do not do so at this temperature on nutrient agar plates.

Electron microscope study of a plasmid chimera containing the replication region of the Escherichia coli F plasmid

“…A tracing ofthe heteroduplex is also shown. Arrows c and d denote the ends ofthe region of homology between pML31 and FA (33)(34)(35)(36)(37)(38)(39)(40)(41)(42)(43). Arrows e and f denote the ends of the inverted repeat ofpML31.…”

“…Furthermore, it seems very unlikely that a sequence that contains the information for the replication functions of F would hybridize to chromosomal sequences of the F', as the second alternative requires. pML31/FA (33)(34)(35)(36)(37)(38)(39)(40)(41)(42)(43) heteroduplex. The location of the hybrid region in pML31/F8-33 as 40.3-49.3F was confirmed by examination of heteroduplexes formed between pML31 and FA (33)(34)(35)(36)(37)(38)(39)(40)(41)(42)(43).…”

“…FA(33-43) is a deletion mutant of F, which is missing the sequence 32.6-42.9F (1); it contains no chromosomal sequences. pML31/ FA (33)(34)(35)(36)(37)(38)(39)(40)(41)(42)(43) heteroduplexes display a duplex region 6.4 + 0.3 kb in length ( Fig. 4, Table 2).…”

“…Therefore, that region of pML31 cannot be homologous to chromo-somal sequences of F8-33 but must be homologous to the F sequences 40.3-49.3F. Since 40.3-49.3F overlaps the 32.6-42.9F deletion of FA (33)(34)(35)(36)(37)(38)(39)(40)(41)(42)(43), it would be expected that the hybrid region of the pML31/FA (33)(34)(35)(36)(37)(38)(39)(40)(41)(42)(43) heteroduplex would be shorter than the hybrid region of the pML31/F8-33 heteroduplex by an amount of (42.9-40.3) or 2.6 kb. Similarly, the longer ofthe two single-stranded regions between the duplex region and the inverted repeat of pML31 should be 2.6 kb longer in the pML31/FA(33-43) heteroduplex than in the pML31/F8-33 heteroduplex.…”

Diameter of cells of a thermosensitive dnaA mutant of Escherichia coli cultivated at intermediate temperatures

“…Both strains are thr leu thi supE and lacY. The source of A3 has been described previously (25). The strains were cultivated in M9 minimal salts medium supplemented with glucose (0.2%), the required L-amino acids (50 jig/ml), biotin (10 Lg/ml), and vitamin-free Casamino Acids (0.5%).…”