Читать книгу Algorithms in Bioinformatics - Paul A. Gagniuc - Страница 18

Promoter and enhancer regions regulate the transcription of nearby genes. The initiation of transcription is conditioned by various regulatory proteins that bind to the regulatory regions of DNA (the promoter and enhancer regions). In eukaryotes, the regulatory proteins facilitate changes in the local chromatin structure to allow proper recruitment and binding of RNA polymerase to one of the DNA strands. Thus, the local chromatin structure either promotes or inhibits RNA polymerase and TF binding. Transcription begins once the RNA polymerase enzyme binds to the promoter region of the gene. Regulatory proteins in conjunction with different combinations of TF dictate the frequency of synthesis for pre-messenger RNA (mRNA) molecules (how many copies per unit of time). For instance, different combinations of TFs lead to different three-dimensional macromolecular conformations (the transcription mediator complex) [42]. These temporary macromolecular constructions (made of TFs and other proteins) and their interaction with chromatin, allow the access of RNA polymerase to the DNA sequence to a greater or lesser extent. The difficulty of recruitment imposes a probability distribution for binding. In turn, this binding probability of RNA polymerase sets the frequency of synthesis for pre-mRNAs. As a rule of thumb, a more open chromatin structure is associated with active gene transcription events, while a more compact chromatin structure indicates transcriptional inactivity (no expression).