Messenger ribonucleic acids (mRNAs) are molecules that represent the intermediate step in the conversion of genetic information carried in a cell's deoxyribonucleic acid (DNA) into functional proteins. They are synthesised by the enzyme RNA polymerase, which recognises specific sequences in the DNA (promoters) to initiate the process called transcription. Downstream sequences, called terminators, provide the signals for transcription to stop. Structural features of mRNAs, such as the presence of a strong ribosome-binding site (RBS) and appropriate spacing between the RBS and the translation start codon, control both how effectively the information they contain is translated into functional proteins and how rapidly they are decayed. The steady-state level of each mRNA, which is determined by the rate of its synthesis versus the rate of its decay, helps regulate how much protein is synthesised from each mRNA. mRNA decay in prokaryotes is carried out by a series of nucleases that can either degrade the RNA molecule by cleaving at internal sites or removing one nucleotide at a time from either the 5' or 3' terminus.