Probe length normalization and quantified gene expression levels in M. tuberculosis. (a) We found that longer probes correlated with increased fluorescent intensities, which then biased the ppm values we obtained. (b) We are able to remove this bias using a model of linear regression. The three distinct groupings visible in the figure are an artifact of the probe lengths targeted during their synthesis by PCR. (c) The level of expression for each gene in the genome, as determined by our analysis from chemostat grown wild-type M. tuberculosis H37Rv, is shown ordered as they appear in the chromosome. (d) The log frequency distribution of mRNA abundances from (c). A clear skew to the right, containing a subset of very highly expressed genes, is typical of the distributions we have found.
Sidders et al. Genome Biology 2007 8:R265 doi:10.1186/gb-2007-8-12-r265