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<p>Bacterial small RNAs have emerged as a class of molecules having important regulatory roles. Accumulating numbers of <em>cis</em>-encoded sRNAs (antisense RNAs) have been recently discovered to be transcribed from the chromosomal DNA of many bacterial species, including the streptomycetes. Here, we investigate potential regulatory roles for two <em>S. coelicolor</em> antisense RNAs, scr4677 and α-abeA.</p> <p>The scr4677 antisense RNA is transcribed from the intergenic region between <em>SCO4676</em> (a gene encoding a conserved protein of unknown function) and <em>SCO4677</em>, encoding a regulatory protein with proposed anti-sigma factor activity. Transcription profiling revealed that scr4677 may not only interact with <em>SCO4676</em> mRNA but also with <em>SCO4677-4676</em> read-through transcripts. Our study suggested that scr4677 functioned to destabilize <em>SCO4676</em> mRNA, at the same time that it stabilized the <em>SCO4677-4676</em> read-through transcript. The potential role for scr4677 in destabilizing <em>SCO4676</em> mRNA was not mediated by the double stranded ribonuclease RNase III. Genetic analysis showed <em>scr4677</em> transcription was affected by SCO4677, and the transcription was apparently dependent on an unknown protein binding to the <em>SCO4676 </em>coding sequence.</p> <p>A second independent study focused on investigating the regulation of a previously uncharacterized genetic region, <em>SCO3287-3290</em>, since renamed <em>abeABCD</em>. This region contains an antisense RNA (α-abeA)-encoding gene, and is adjacent to the downstream <em>SCO3291</em> (<em>abeR</em>) gene, which encodes a putative regulatory protein. Genetic analysis revealed that overexpression of <em>abeR </em>or <em>abeABCD</em> stimulated the production of the blue-pigmented antibiotic actinorhodin, and deletion of <em>abeR</em> impaired actinorhodin production. Transcription analysis revealed the <em>abe</em> genes (including α-<em>abeA</em>) to be subject to multiple levels of regulation. We found an internal promoter within the <em>abeA</em> coding sequence and that required AbeR for expression. Furthermore, biochemical experiments demonstrated that AbeR regulated <em>abeBCD</em> directly, by binding to four heptameric repeats in its promoter region. The expression of α-<em>abeA</em> and other <em>abe</em> genes were differentially affected by RNase III.</p> / Doctor of Science (PhD)