THE CONTRAHELICASE ACTIVITIES OF THE REPLICATION TERMINATOR PROTEINS OF ESCHERICHIA-COLI AND BACILLUS-SUBTILIS ARE HELICASE-SPECIFIC AND IMPEDE BOTH HELICASE TRANSLOCATION AND AUTHENTIC DNA UNWINDING
T. Sahoo et al., THE CONTRAHELICASE ACTIVITIES OF THE REPLICATION TERMINATOR PROTEINS OF ESCHERICHIA-COLI AND BACILLUS-SUBTILIS ARE HELICASE-SPECIFIC AND IMPEDE BOTH HELICASE TRANSLOCATION AND AUTHENTIC DNA UNWINDING, The Journal of biological chemistry, 270(49), 1995, pp. 29138-29144
Replication forks are arrested at sequence-specific replication termin
i primarily, perhaps exclusively, by polar arrest of helicase-catalyze
d DNA unwinding by the terminator protein. The mechanism of this arres
t is of considerable interest. This paper presents experimental eviden
ce in support of four major points pertaining to termination of DNA re
plication. First, the replication terminator proteins of both Escheric
hia coli and Bacillus subtilis are helicase-specific contrahelicases,
i.e. the proteins specifically impede the activities of helicases that
are involved in symmetric DNA replication but not of those involved i
n conjugative DNA transfer and rolling circle replication. Second, the
terminator protein (Ter) of E. coli blocks not only helicase transloc
ation but also authentic DNA unwinding. Third, the replication termina
tor protein of Gram-positive B. subtilis is a polar contrahelicase of
the primosomal helicase PriA of Gram-negative E. coli. Finally, the bl
ockage of PriA-catalyzed DNA unwinding was abrogated by the passage of
an RNA transcript through the replication terminator protein-terminus
complex. These results are significant because of their relevance to
the mechanistic aspects of replication termination.