Multiple transcript initiation as a mechanism for regulating gene expression

Transcription is the intermediary process that copies a DNA-encoded gene into a form which is either functional in its own right (stable RNAs, such as ribosomal or transfer RNAs) or can be decoded by the translational machinery into a functional protein. Transcripts destined for translation are called messenger RNAs (mRNAs), since they act as go-betweens from DNA to protein. Although RNAs are transcribed as single-stranded molecules, most can assume complicated secondary and tertiary structures that are critical for proper functioning. As a result, each mRNA contains not only the sequence information required to synthesize a protein, but also structural components that can regulate mRNA localization, stability, and translation efficiency. Thus the initiation of transcription occupies a preeminent place in the regulation of gene expression.