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Restriction alleviation and modification enhancement by the Rac prophage of Escherichia coli K‐12
Author(s) -
King Gareth,
Murray Noreen E.
Publication year - 1995
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1111/j.1365-2958.1995.tb02438.x
Subject(s) - biology , prophage , plasmid , escherichia coli , lambda phage , mutant , genetics , gene , bacteriophage , mutagenesis , function (biology) , restriction site , microbiology and biotechnology , restriction enzyme
Summary Bacteriophage λ. encodes an antirestriction function, Ral, which is able to modulate the activity of the Escherichia coli K‐12 restriction and modification system, EcoKl. Here we report the characterization of an analogous function, Lar, expressed by E. coli sbcA mutants and the hybrid phage λreverse. E. coli sbcA mutants and λ.reverse both express genes of the Rac prophage, and we have located the lar gene immediateiy downstream of recT in this element. The lar gene has been cloned in an expression plasmid, and a combination of site‐directed mutagenesis and labelling of plasmid‐encoded proteins has enabled us to identify a number of translational products of lar, the smallest of which is sufficient for restriction alleviation. Lar, like Ral, is able both to alleviate restriction and to enhance modification by Eco Kl. Lar, therefore, is functionally similar to Ral and the nucleotide sequences of their genes share 47% identity, indicating a common origin. A comparison of the predicted amino acid sequences of Lar and Ral shows only a 25% identity, but a few short regions do align and may indicate residues important for structure and/or function.