Small RNAs in Rickettsia:: are they functional?

Many obligate intracellular pathogens have small genomes with high fractions of pseudogenes. A recent analysis of gene expression patterns in Rickettsia conorii shows that short open reading frames inside deteriorating genes are occasionally transcribed into RNA. Here, we show that substitution frequencies at nonsynonymous sites are similar for expressed and unexpressed parts of the fragmented genes. We conclude that the observed expression is a temporary stage in the gene degradation process, suggesting that the expressed gene fragments are not functional.