1887

Abstract

encodes an adhesin of and has been implicated in filamentation and virulence. , an often-used transformation selection marker, is apparently incorrectly expressed when integrated at the locus, which results in an attenuated virulence phenotype. Expression of is compromised by ectopic integration at other loci as well. In contrast, prior studies from the authors' laboratory had demonstrated that the filamentation deficiency and attenuated virulence of Δ mutants were fully restored in rescued strains in which was integrated at the locus. This discrepancy prompted a reinvestigation of these mutants. A series of congenic strains were constructed which demonstrated that the filamentation and virulence defects of a homozygous Δ mutant could be rescued without introduction of a functional allele. Despite the absence of detectable differences in expression, analysis of suppressor mutations suggested that reduced expression gave rise to the mutant phenotypes. Several independent spontaneous suppressor mutations that restored filamentation to strains of genotype Δ : : /Δ : :  had acquired a tandem duplication of the marker cassette. The null mutant and rescued strains differed by the presence or absence of flanking sequence. Substitution of the insert of the null mutant with alone largely rescued the filamentation and virulence phenotypes. The presence of a single copy of adjacent to had no effect. It is concluded that flanking direct repeats of , present as part of a recyclable disruption cassette, negatively influenced expression and are responsible for the previously reported phenotypes of the mutants.

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2005-04-01
2020-09-27
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