transcription of the genes in one operon - (Apr/12/2007 )

Hi, all,
I got one question to ask---there are 4 genes in one operon that I am working on. But it turns out that transcription level of the 2nd, 3rd and 4th are even higher than (e.g 2 fold higher, as readings from Affymetrix array data) that of the 1st one. Is it possible?
what are the potential reasons?

The obvious one I can think of is maybe the last three genes have their own hidden promoters. any other reasons?

thanks,

VF

Would also guess on promoter sequences. Another possibility - different chromatin structure - histone modifications and DNA methylation (that can also occur in exons). Do your findings hold real-time validation?
K.