Sh. Chai et al., BACILLUS-SUBTILIS BACTERIOPHAGE-SPP1 TERMINASE HAS A DUAL ACTIVITY - IT IS REQUIRED FOR THE PACKAGING INITIATION AND REPRESSES ITS OWN SYNTHESIS, Gene, 184(2), 1997, pp. 251-256
The B. subtilis bacteriophage SPP1 terminase, encoded by genes 1 and 2
, is required for the initiation of headful packaging. The DNA segment
to which gene 1 product (GIP) binds includes the pact and pacR sites
and the late PL1 and PL2 promoters from which genes 1 to 7 are transcr
ibed. When SPP1wt or SPP1sus115 (gene 6(-)) phages were used to infect
a B. subtilis sup(0) strain, the gene 1 to 7 mRNA synthesis was reduc
ed at late times of infection. This was not observed, however, when ei
ther chloramphenicol was added 7 min after infection with SPP1wt or wh
en SPP1sus114 (gene 1(-)) or SPP1sus19 (gene 2(-)) were used to infect
B. subtilis sup(0) cells. These results suggest that the terminase en
zyme functions as a repressor of its own transcription. G1P and B. sub
tilis RNA polymerase (RP) bind to the pact segment, which contains the
PL1 and PL2 promoter region. The binding of G1P to the pact site does
not seem to exclude RP from the promoters, despite of the overlapping
of their binding sites. It is likely that the terminase protein does
not repress transcription by a mere steric hindrance of RP binding.