Sequence changes in coliphage lambda mutants affecting the nutL antitermination site and termination by tL1 and tL2.

Area of Science:

• Molecular Biology
• Genetics
• Virology

Background:

• Coliphage lambda utilizes N-mediated antitermination for transcription regulation.
• The nutL site is essential for this antitermination process in the major leftward operon.

Purpose of the Study:

• To investigate the structural and functional significance of the nutL sequence.
• To characterize mutations affecting nutL function and identify revertant mechanisms.

Main Methods:

• Isolation and characterization of spontaneous nutL mutants in coliphage lambda.
• Analysis of nucleotide changes within the nutL hairpin structure.
• Investigation of second-site revertants, including large deletions.

Main Results:

• Mutations in the nutL loop (guanine to adenine, thymine, or cytosine) abolish antitermination.
• A mutation in the stem destabilized the hairpin structure.
• True reversions restored the original guanine, while a second-site deletion created an active, fused N-product.

Conclusions:

• The nutL hairpin structure, particularly the loop region, is critical for N-mediated antitermination.
• Genetic alterations can either disrupt or restore nutL function, highlighting the sequence's regulatory role.
• Deletions can bypass the requirement for a functional nutL site by creating active fusion proteins.