[Identification in vivo of promoter activity in the left site of the att region of bacteriophage lambda DNA].

The promoter-probing vector (pSK plasmid) was explored for cloning of the fragments from lambda cI857 and lambda b2 DNAs containing different regions of the att site. We have constructed all-tet fusions where the fusions are: 1) HindIII/BamHI-491 base pairs (b. p.) fragment of lambda cI857 DNA containing POP' site (plasmid pSK-PP'); 2) AluI-242 b. p. fragment of lambda cI857 DNA containing the left arm of the POP' site (plasmid pSK-P); 3) AluI-242 b. p. fragment of lambda cI857 DNA with opposite orientation (plasmid pSK-P); 4) EcoRI/BamHI-750 b. p. fragment of lambda b2 DNA containing the right arm of the POP' site (plasmid pSK-P'). These fusions permit us to analyse the effect of various pieces of the attachment site on the expression tet gene as the result of reparation of this gene promoter. We find that expression of tet (tetracycline resistant phenotype) takes place in the pSK-PP' and pSK-P but not in the pSK-P' and pSK-P. These facts permit us to conclude that the left arm of the att site contains a rightward promoter functioning in vivo. We postulate that this promoter activity might correspond to the promoter patt, which was described in previous experiments in vitro.