Characterization of a temperature-sensitive DNA ligase from Escherichia coli.
DNA ligases are essential enzymes in cells due to their ability to join DNA strand breaks formed during DNA replication. Several temperature-sensitive mutant strains of Escherichia coli, including strain GR501, have been described which can be complemented by functional DNA ligases. Here, it is shown that the ligA251 mutation in E. coli GR501 strain is a cytosine to thymine transition at base 43, which results in a substitution of leucine by phenylalanine at residue 15. The protein product of this gene (LigA251) is accumulated to a similar level at permissive and non-permissive temperatures. Compared to wild-type LigA, at 20 degrees C purified LigA251 has 20-fold lower ligation activity in vitro, and its activity is reduced further at 42 degrees C, resulting in 60-fold lower ligation activity than wild-type LigA. It is proposed that the mutation in LigA251 affects the structure of the N-terminal region of LigA. The resulting decrease in DNA ligase activity at the non-permissive temperature is likely to occur as the result of a conformational change that reduces the rate of adenylation of the ligase.
Lavesa-Curto
Manuel
M
School of Biological Sciences, University of East Anglia, Norwich NR4 7TJ, UK.
Sayer
Heather
H
Bullard
Desmond
D
MacDonald
Andrew
A
Wilkinson
Adam
A
Smith
Andrew
A
Bowater
Laura
L
Hemmings
Andrew
A
Bowater
Richard P
RP
D000595:Amino Acid Sequence; D011088:DNA Ligases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D004926:Escherichia coli / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development; D029968:Escherichia coli Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation; D013696:Temperature
D029968:Escherichia coli Proteins; D011088:DNA Ligases; C120640:DNA ligase (NAD); C497118:LigA protein, E coli