A comparative analysis of the occurrence frequency of oligonucleotides in two sets of yeast genes with higher and lower transcription frequencies respectively has shown that the sequence structures of the two sets of introns are different. There are more potential binding sites in the introns of genes with higher transcription frequencies. After observing regulatory sites obtained by experimental analysis, many transcriptional regulatory sites in yeast consist of a pair of highly conserved oligonucleotides, spaced by a non-conserved region of fixed width (dyad). Therefore, dyad-like transcriptional regulatory sites are analyzed. Some dyads are extracted by statistical comparative analysis of the occurrence frequencies, whose occurrence frequencies in the set of introns with higher transcription frequencies are higher significantly than those in the set of introns with lower transcription frequencies. Analyzing the distribution of the extracted dyads in two sets of introns, and comparing with the regulatory sites revealed by experiments, these dyads are probably related to positive transcriptional regulation.