MOLECULAR-BIOLOGY OF MYCOPLASMAS

Citation
K. Dybvig et Ll. Voelker, MOLECULAR-BIOLOGY OF MYCOPLASMAS, Annual review of microbiology, 50, 1996, pp. 25-57
Citations number
210
Language
INGLESE
art.tipo
Review
Categorie Soggetti
Microbiology
ISSN journal
0066-4227
Volume
50
Year of publication
1996
Pages
25 - 57
Database
ISI
SICI code
0066-4227(1996)50:<25:MOM>2.0.ZU;2-5
Abstract
Although mycoplasmas lack cell walls, they are in many respects simila r to the gram-positive bacteria with which they share a common ancesto r. The molecular biology of mycoplasmas is intriguing because the chro mosome is uniquely small (< 600 kb in some species) and extremely A-T rich (as high as 75 mol% in some species). Perhaps to accommodate DNA with a lower G + C content, most mycoplasmas do not have the ''univers al'' genetic code. In these species, TGA is not a stop codon; instead it encodes tryptophan at a frequency 10 times greater than TGG, the us ual codon for this amino acid. Because of the presence of TGA codons, the translation of mycoplasmal proteins terminates prematurely when cl oned genes are expressed in other eubacteria, such as Escherichia coli . Many mycoplasmas possess strikingly dynamic chromosomes in which hig h-frequency changes result from errors in DNA repair or replication an d from highly active recombination systems. Often, high-frequency chan ges in the mycoplasmal chromosome are associated with antigenic and ph ase variation, which regulate the production of factors critical to di sease pathogenesis.