Specialized transducing phages lambda asn harboring chromosomal DNA and genetic markers on either side of the asn gene were isolated. Phages carrying chromosomal DNA counterclockwise of the asn gene can upon infection establish themselves as self-replicating plasmids in asn, recA hosts lysogenic for lambda. It is concluded that this bypassing of normal lambda immunity is due to the presence of the chromosomal replication origin, oriC, in this class of phages. Genetic analysis and the determination of restriction endonuclease cleavage patterns of the different lambda asn lead to the allocation of oriC within 1.5 megadaltons of the asn gene towards the uncA, uncB genes at 82 min on the genetic map of E. coli. The clockwise order of genes on the chromosomes is found to be: bglB, (pst, glmS), (uncA, uncB), oriC, asn, trkD, rbs, rrnC, ilv.

A precise genetic-physical map of the tna-ilv region at 82 min on the genetic map of E. coli is obtained through deletion mapping and analysis by restriction endonuclease EcoRI of plasmids, derived from an F' carrying the genes between aroE and ilv. A locus, designated het, which in its diploid state results in slow growth and heterogeneity of cell size due to distorted cell division, maps between bglB and asn, 30-45 kb counterclockwise of ilv. The pattern of R.EcoRI cleavage sites in the het region is identical with the pattern obtained by Marsh and Worcel (1977) who analyzed DNA labeled preferentially in the region of the DNA replication origin (oriC). We suggest that oriC is identical with the het site and that it can be allocated to a position 32 kb counterclockwise of the ilv operon.

Growth of the permeable strain AS19 of Escherichia coli B is more sensitive to the antibiotic streptolydigin than is in vitro ribonucleic acid (RNA) synthesis. The in vivo chain elongation rates of lacZ messenger RNA and ribosomal RNA are not affected at 1.5 x 10-6 M, a concentration that reduces the growth rate threefold. The synthesis of large proteins is inhibited preferentially, and a considerable fraction of the polypeptides synthesized is unstable. The synthesis of complete ,8-galactosidase is inhibited relative to the synthesis of short, unstable polypeptides, which include the first 60 to 70 amino acids of /3-galactosidase. The expression of the following polycistronic transcription units is strongly biased against promoter-distal genes: trp, deo, rpoBC, and rrn. The extent of polarity is proportional to the distance transcribed and to the streptolydigin concentration. Streptolydigin appears to destabilize active transcription complexes irreversibly irrespective of the type of transcript (messenger RNA, ribosomal RNA) and of transcription intensity. We suggest that streptolydigin leads to premature termination of transcription, resulting in release of incomplete transcripts and, thus, a decrease in overall messenger RNA concentration, which becomes limiting for protein synthesis, i.e., for growth.The antibiotic streptolydigin interferes with bacterial ribonucleic acid (RNA) synthesis in vivo and in vitro (32, 34). Mutations to streptolydigin resistance are located in the /B subunit of the RNA polymerase (13,16,32). Together with biochemical evidence (5, 34) this indicates that streptolydigin inhibits RNA synthesis by interaction with the RNA polymerase rather than by binding to the template as does actinomycin D (27). In contrast to rifampin, which acts on initiation of transcription (36, 41), streptolydigin has been shown to interfere with RNA chain elongation (5). Cassani et al. (5) also showed stabilization of the RNA-enzyme-deoxyribonucleic acid (DNA) complex in vitro when using purified RNA polymerase and T4 DNA; the inhibition of RNA chain elongation is reversible in vitro (34).In attempts to apply these in vitro results in vivo, we realized that the effects of streptlydigin