In bacteria, genes within an operon are transcribed under the control of a single promoter and the primary mRNA transcript contains sequences that can be translated into each of the independent proteins. In some cases the first gene in the linear sequence appears to be transcribed at a much higher rate than the second and subsequent genes (i.e. many but not all mRNAs contain the sequences encoded by gene 2 and beyond).
What kind of DNA sequences might be present between the first and second genes to account for this discrepancy on transcript numbers?