  We discuss two new approaches to extract relevant biological information on
the Transcription Factors (and in particular to identify their binding
sequences) from the statistical distribution of oligonucleotides in the
upstream region of the genes. Both the methods are based on the notion of a
``regulatory network'' responsible for the various expression patterns of the
genes. In particular we concentrate on families of coregulated genes and look
for the simultaneous presence in the upstream regions of these genes of the
same set of transcription factor binding sites. We discuss two instances which
well exemplify the features of the two methods: the coregulation of glycolysis
in Drosophila melanogaster and the diauxic shift in Saccharomyces cerevisiae.
