Applications of recombinant DNA technology in gastrointestinal medicine and hepatology: Basic paradigms of molecular cell biology. Part B: Eukaryoticgene transcription and post-transcriptional RNA processing

The transcription of DNA into RNA is the primary level at which gene expres sion is controlled in eukaryotic cells. Eukaryotic gene transcription invol ves several different RNA polymerases that interact with a host of transcri ption factors to initiate transcription. Genes that encode proteins are tra nscribed into messenger RNA (mRNA) by RNA polymerase II. Ribosomal RNAs (rR NAs) and transfer RNAs (tRNAs) are transcribed by RNA polymerase I and III, respectively. The production of each mRNA in human cells involves complex interactions of proteins (ie, trans-acting factors) with specific sequences on the DNA (ie, cis-acting elements). Cis-acting elements are short base s equences adjacent to or within a particular gene. While the regulation of t ranscription is a pivotal step in the control of gene expression, a variety of molecular events, collectively known as 'RNA processing' add an additio nal level of control of gene expression in eukaryotic cells.