The present invention provides
nucleic acid molecules,
DNA constructs, plasmids, and methods for post-
transcriptional regulation of
gene expression using
RNA molecules to both repress and activate translation of an
open reading frame. Repression of
gene expression is achieved through the presence of a regulatory
nucleic acid element (the cis-repressive
RNA or crRNA) within the 5′
untranslated region (5′ UTR) of an mRNA molecule. The
nucleic acid element forms a hairpin (stem / loop) structure through complementary base
pairing. The hairpin blocks access to the mRNA transcript by the
ribosome, thereby preventing translation. In particular, in embodiments of the invention designed to operate in
prokaryotic cells, the stem of the hairpin secondary structure sequesters the
ribosome binding site (RBS). In embodiments of the invention designed to operate in eukaryotic cells, the stem of the hairpin is positioned upstream of the
start codon, anywhere within the 5′ UTR of an mRNA. A
small RNA (trans-activating
RNA, or taRNA), expressed in trans, interacts with the crRNA and alters the hairpin structure. This alteration allows the
ribosome to
gain access to the region of the transcript upstream of the
start codon, thereby activating transcription from its previously repressed state.