Bifractality of human DNA strand-asymmetry profiles results from transcription

We use the wavelet transform modulus maxima method to investigate the multifractal properties of strand-asymmetry DNA walk profiles in the human genome. This study reveals the bifractal nature of these profiles, which involve two competing scale-invariant (up to repeat-masked distances less than or similar to 40 kbp) components characterized by Holder exponents h(1)=0.78 and h(2)=1, respectively. The former corresponds to the long-range-correlated homogeneous fluctuations previously observed in DNA walks generated with structural codings. The latter is associated with the presence of jumps in the original strand-asymmetry noisy signal S. We show that a majority of upward (downward) jumps colocate with gene transcription start (end) sites. Here 7228 human gene transcription start sites from the refGene database are found within 2 kbp from an upward jump of amplitude Delta S >= 0.1 which suggests that about 36% of annotated human genes present significant transcription-induced strand asymmetry and very likely high expression rate.