Journal of General Virology, Vol 79, 205-210, Copyright © 1998 by Society for General Microbiology
Identification of an early positive regulatory gene of mycobacteriophage L1
HJ Datta and NC Mandal
Department of Biochemistry, Bose Institute, Calcutta, India.
Among 14 temperature-sensitive, growth-defective mutants of
mycobacteriophage L1 showing a lysis-defective phenotype at 42 degrees C,
six are, in addition, defective in phage DNA synthesis at 42 degrees C. In
the present study, we show that one of the latter six mutants, L1G27ts901,
is also defective in the synthesis of both an L1-specific exonuclease (a
representative delayed early protein), and of RNA in both the delayed early
and late periods but not in the immediate early period. The results of a
temperature-shift experiment suggest that the synthesis of L1 exonuclease
is regulated by G27 at the level of transcription. Furthermore, the
temperature-sensitive defect in delayed early and late RNA synthesis could
be largely overcome when the L1G27ts901-infected culture was shifted from
32 to 42 degrees C at 10 min but not at zero time post-infection. These
results suggest that the primary effect of the G27ts901 mutation is to make
the phage defective in transcription of delayed early genes at 42 degrees
C, and the defect in late RNA synthesis by this mutant is a secondary
effect which is caused by its inability to express regulatory gene
products. We conclude that G27 is involved in the positive regulation of
expression of the delayed early genes of L1 at the transcriptional level.
