title: [Strong strand specific composition bias-a genomic character of some obligate parasites or symbionts].
abstract: DNA replication includes a set of asymmetric mechanisms, which is a division into lagging and leading strands. The former is synthesized continuously whereas the synthesis for the latter is discontinuous. Such a asymmetric mechanism leads to distinct nucleotide composition of these two strands. Strands specific nucleotide composition bias was originally found in genomes of echinoderm and vertebrate mitochondria and then in several bacterial genomes. With the rapid growth in the number of sequenced genomes, many bacteria and even eukaryotes are found to have the consistent strand composition bias. In some bacteria, the extent of strand specific composition bias was so strong that genes on the two replicating strands could be separated according to their codon usages. Till now, 11 obligate intracellular bacteria have been found to have separate codon usages according to whether genes located on the leading or lagging strands. However, there is still not a well-accepted theory that could interpret the reason for the occurrence of separate codon usages in some special bacterial genomes and not in others. This paper reviews the related works and points out its open problems.
authors: University of Electronic Science and Technology of China, Chengdu, China. fbguo@uestc.edu.cn
authors: Feng-Biao
authors: FB
authors: Guo
mesh_terms: D001419:Bacteria / Q000235:genetics*; D001482:Base Composition; D003062:Codon; D004261:DNA Replication; D023281:Genomics; D013559:Symbiosis / Q000235:genetics*
chemical_list: D003062:Codon