Deviations from Chargaff's 2nd parity rule, according to which A approximately T 
and G approximately C in single stranded DNA, have been associated with 
replication as well as with transcription in prokaryotes. Based on observations 
regarding mainly the transcription-replication co-linearity in a large number of 
prokaryotic species, we formulate the hypothesis that the replication procedure 
may follow different modes between genomes throughout which the skews clearly 
follow different patterns. We draw the conclusion that multiple functional sites 
of origin of replication may exist in the genomes of most archaea and in some 
exceptional cases of eubacteria, while in the majority of eubacteria, 
replication occurs through a single fixed origin.