Читать книгу Neurobiology For Dummies - Frank Amthor - Страница 60

The classic picture of DNA being transcribed to RNA, and RNA being translated into proteins, was typically thought of as a one-way process. However, this description is not complete. The products of DNA expression, as well as external substances that get taken up by a cell, can also regulate protein production.

One example of the backward flow of information (or backward synthesis) is reverse transcription, which is the transfer of information from RNA to make new DNA. Reverse transcription occurs in retroviruses such as HIV and is a common feature of the replication cycle for many viruses. The main function of many proteins synthesized from DNA is to regulate DNA expression, typically by modulating methylation and histone acetylation (refer to “Gene regulation,” earlier in this chapter). The expression of DNA can even be regulated by sequences within the DNA itself. For example, some introns enhance the expression of the gene in which they dwell through a process called intron-mediated enhancement. More generally, introns may have short sequences that are important for efficient splicing by spliceosomes.