T4 late transcripts are initiated near a conserved DNA sequence

Area of Science:

• Microbiology
• Molecular Biology
• Genetics

Background:

• Bacteriophage T4 late transcription is complex, differing from typical prokaryotic systems.
• It necessitates host RNA polymerase, specific T4 proteins (genes 33, 45, 55), and unidentified polypeptides.
• DNA template competency, involving 5-hydroxymethyl cytosine and replication, is essential for late transcription.

Purpose of the Study:

• To map the initiation sites of messenger RNAs (mRNAs) for four Bacteriophage T4 late genes (21, 22, 23, 36) in vivo.
• To determine the DNA sequences at these initiation sites.
• To investigate the role of DNA replication in late transcription.

Main Methods:

• S1 nuclease mapping was employed to locate mRNA initiation sites.
• DNA sequencing was performed at the identified initiation sites.
• Analysis of gene 23 mRNA synthesis in a DNA replication-deficient mutant (genes 30 and 46) was conducted.

Main Results:

• The initiation sites for T4 late mRNAs from genes 21, 22, 23, and 36 were mapped.
• A conserved DNA sequence, TATAAATACTATT, was identified upstream of the 5' ends of late mRNAs.
• Gene 23 mRNA synthesized in the absence of DNA replication was identical to the normal late transcript.

Conclusions:

• The conserved sequence TATAAATACTATT is likely recognized by the transcription machinery for Bacteriophage T4 late gene expression.
• Late transcription can be initiated independently of DNA replication under specific mutant conditions.
• These findings elucidate key regulatory elements of complex viral gene expression.