Removal of a terminator structure by RNA processing regulates int gene expression

Area of Science:

• Molecular Biology
• Genetics
• Virology

Background:

• The int gene of bacteriophage lambda is crucial for site-specific recombination.
• Lambda phage gene expression is tightly regulated during its infective cycle.
• Two promoters, pL and pI, control int gene transcription, requiring different activation factors (lambda N and cII proteins).

Purpose of the Study:

• To investigate the differential regulation of the int gene during the lambda infective cycle.
• To elucidate the mechanism of negative control over int gene expression.
• To understand the role of RNase III and the sib site in retroregulation.

Main Methods:

• Analysis of int gene transcription from pL and pI promoters.
• In vivo and in vitro studies of RNase III activity on lambda transcripts.
• Investigation of gene expression in RNase III-deficient (rnc-) hosts.
• Cloning of the sib site downstream of a bacterial gene to assess its regulatory function.

Main Results:

• RNase III processes pL transcripts at the sib site, preventing int gene product synthesis.
• pI transcripts are terminated and unprocessed, allowing int gene expression.
• Unprocessed pL transcripts in rnc- hosts can express int, confirming RNase III's role.
• The sib site demonstrates retroregulatory control over a cloned bacterial gene.

Conclusions:

• RNase III-mediated processing at the sib site (retroregulation) is a key mechanism for negative control of lambda int gene expression.
• This processing prevents the synthesis of the int gene product from early, read-through pL transcripts.
• Retroregulation by the sib site is a general mechanism applicable to other genes beyond the int gene.