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Antigenic variation can result from gene conversion, [1] site-specific DNA inversions, [2] hypermutation, [3] or recombination of sequence cassettes. [4] The result is that even a clonal population of pathogens expresses a heterogeneous phenotype. [5] Many of the proteins known to show antigenic or phase variation are related to virulence. [6]
Phase variation slipped strand mispairing. Altered gene expression is a result of SSM and depending where the increase or decrease of the short repeat sequences occurs in relation to the promoter will either regulate at the level of transcription or translation. [8] The outcome is an ON or OFF phase of a gene or genes.
English: Phase and Antigenic Variation in Bacteria. pA is the promoter for FimA, pB is the promoter for FimB and pE is the promoter for FimE. IRR is inverted repeat right and IRL is inverted repeat left.
However, in many bacterial pathogens, mod genes contain simple sequence repeats (SSRs), and the associated restriction enzyme encoding gene (res) is inactive. In these organisms the DNA methyltransferase phase varies between two states (ON or OFF) by variation in the number of SSRs in the mod gene. [9] Multiple different mod genes have been ...
Since Salmonella typically exhibit phase variation between two motile phenotypes, [3] different "H" antigens may be expressed. Salmonella that can express only one "H" antigen phase consequently have motile and non-motile phenotypes and are termed monophasic, whilst isolates that lack any "H" antigen expression are termed non-motile. [ 4 ]
Phase variation is similar to antigenic variation, but instead of changes at the genetic level altering the composition of molecules, these genetic changes result in the activation or deactivation of a gene. [9] Phase variation most often arises from a frameshift in the expressed gene. [9]
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As argued in Ch. 5 of Stoltzfus 2021, [43] various mechanisms of mutation in pathogenic microbes, e.g., mechanisms for phase variation and antigenic variation, appear to have evolved so as to enhance lineage survival, and these mechanisms are routinely described as strategies or adaptations in the microbial genetics literature, such as by Foley ...