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J. Bacteriol., Dec 1995, 6881-6893, Vol 177, No. 23
S Karlin, GM Weinstock and V Brendel
RecA protein sequences from 62 eubacterial sources were compared with one
another and relative to one archaebacterial RecA-like and a number of
eukaryotic RecA-like sequences. Pairwise similarity scores were determined
by a novel method based on significant segment pair alignment. The
sequences of different species were grouped on the basis of mutually high
similarity scores within groups and consistency of score ranges in
comparison to other groups. Following this protocol, the
gamma-proteobacteria can be subclassified into two major groups, those of
mostly vertebrate hosts and those of mostly soil habitat. The
alpha-proteobacterial sequences also divide into two distinct groups,
whereas classification of the beta-proteobacteria is more complex. The
gram-positive bacterial sequences split into three groups of low and three
groups of high G+C genome content. However, neither the combined
low-G+C-content nor the combined high-G+C-content group nor the aggregate
of all gram-positive bacteria form homogeneous groups. The mycoplasma
sequences score best with the Bacillus subtilis sequence, consistent with
their presumed origin from a gram-positive ancestor. The eukaryotic RAD
proteins generally show a single high-scoring segment pair with the
proteobacterial RecA sequences around the ATP- binding domain. The
bacteriophage T4 UvsX protein aligns best with RecA sequences on two
segments disjoint from the ATP-binding domain. The distribution of the most
highly conserved regions shared between RecA and noneubacterial RecA-like
sequences suggests a mosaic character and evolution of RecA. The discussion
considers some questions on the validity and consistency of bacterial
classifications derived from RecA sequence comparisons.
Copyright © 1995, American Society for Microbiology
Bacterial classifications derived from recA protein sequence comparisons
Department of Mathematics, Stanford University, California 94305-2125, USA.
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