Unusual insertion element polymorphisms in the promoter and terminator regions of the mucAB-like genes of R471a and R446b.
We have previously identified umu-complementing genes on two incL/M plasmids, R471a and R446b (C. Ho et al., J. Bacteriol., 175 (1993) 5411-5419). Molecular analysis of these genes revealed that they are more structurally and functionally related to mucAB from the incN plasmid pKM101 than to other members of the previously identified Umu-like family. As a consequence, we have termed these new homologs mucAB(R471a) and mucAB(R446b) respectively. Interestingly, while the location of the mucAB-like genes is essentially the same in both R471a and R446b, the regions immediately flanking the mucAB-like genes are highly polymorphic. For example, 5' to mucAB(R471a) we found an insert that appears to be a novel retroelement encoding a putative reverse transcriptase (RT). This RT is related to the reverse transcriptases encoded by group II introns but is embedded in a retron-like context. Immediately 3' to the mucAB(R471a) locus is a putative insertion element of a sparsely-dispersed class not previously reported from enteric bacteria. Both the RT and insertion element are absent in R446b. These observations suggest that the mucAB-like genes from R471a and R446b are located within regions of the R-plasmids that perhaps were once (or still are) mobile genetic elements. Such observations might help explain the distribution of umu-like genes on R-plasmids and bacterial chromosomes.
Kulaeva
O I
OI
Section on DNA Replication, Repair and Mutagenesis, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892-2725, USA.
Koonin
E V
EV
Wootton
J C
JC
Levine
A S
AS
Woodgate
R
R
D000595:Amino Acid Sequence; D016282:Aspartic Acid Endopeptidases / Q000235:genetics; D001426:Bacterial Proteins / Q000235:genetics*; D001483:Base Sequence; D004251:DNA Transposable Elements / Q000235:genetics*; D004269:DNA, Bacterial; D004926:Escherichia coli / Q000235:genetics; D029968:Escherichia coli Proteins; D008969:Molecular Sequence Data; D009876:Operon; D010641:Phenotype; D011110:Polymorphism, Genetic; D011401:Promoter Regions, Genetic; D012194:RNA-Directed DNA Polymerase / Q000235:genetics; D017386:Sequence Homology, Amino Acid; D013728:Terminator Regions, Genetic
D001426:Bacterial Proteins; D004251:DNA Transposable Elements; D004269:DNA, Bacterial; D029968:Escherichia coli Proteins; C068606:mucAB protein, E coli; D012194:RNA-Directed DNA Polymerase; D016282:Aspartic Acid Endopeptidases; C095652:signal peptidase II