INTERFERENCE OF P-R-BOUND RNA-POLYMERASE WITH OPEN COMPLEX-FORMATION AT P-RM IS RELIEVED BY A 10-BASE PAIR DELETION BETWEEN THE 2 PROMOTERS

Bacteriophage lambda promoters P-R and P-RM direct RNA synthesis in di vergent orientations from start sites 82 base pairs apart, We had prev iously determined that the presence on the same DNA fragment of a wild type P-R promoter interfered with the utilization of the P-RM promote r, The results reported here concern the effects of changing the dista nce between the start sites by insertion or deletion of 5 or 10 base p airs. Three different techniques (run-off transcription, gel mobility shift, and permanganate probing) were employed to monitor complex form ation at P-RM. Unexpectedly we find that deletion of 10 base pairs bet ween the start sites abolishes the interference, whereas insertion of 10 base pairs does not, Deletion of 5 base pairs, however, essentially prevents joint complex formation at P-R and P-RM. These findings sugg est several ways in which for the wild type separation of the two prom oters the utilization of P-RM could be affected by an RNA polymerase a t P-R. In addition to direct steric interference, these include the ob struction of access to DNA sites necessary for optimal contact with th e RNA polymerase.