MOLLERACH Marta Eugenia
capítulos de libros
A functional analysis of the Streptococcus pneumoniae genes involved in the synthesis of type1and type 3 capsular polysaccharides.
GARCÍA E; ARRECUBIETA C; MUÑOZ R; MOLLERACH M; LÓPEZ R
Streptococcus pneumoniae, Molecular Biology and Mechanisms of Disease
Mary Ann Liebert, Inc. publishers,
Lugar: New York, USA; Año: 2000; p. 139 - 154
Type 3 pneumococci produce a capsule componed of cellobiuronic acid units connected in a beta (1-3) linkage. Cellobiuronic acid is a disaccharide consisting of D-glucuronic acid (GlcA) beta (1-4) linked to D-glucose (GLc). The genes implicated in the byosynthesis of the type 3 capsule have been cloned, expressed and biochemically characterized. The three type 3-specific genes designated as cap 3ABC- are tramscribed together. However the two complete open reading frames located upstream of cap3A are not transcribed and, consequently are not required for capsule formation. The promoter of the cap3 operon was localized by primer extension analysis. The product of cap3A, cap3B and cap3c were biochemically characterized as a UDP-Glc dehydrogenase, the type 3 polysaccharide synthase, and a Glc-1-P uridyltransferase, respectively. The Cap3B synthase was expressed in Escherichia coli, and pneumococcal type 3 polysaccharide was synthesized in this heterologous system. When a recombinant plasmid (pLSE3B) containing cap3B was introduced by transformation into encapsulated pneumococci of types 1,2,5 or 8, the lyncomicyn-resistant transformants displayed a binary tyoe of capsule, this is, they showd a type 3 capsule in addition to that of the recipient type. Unencapsulated (S2) laboratory strains of S. pneumoniae also synthesized a type 3 capsule when transformed with pLSE3B. On the other hand, we have cloned and sequenced seven type 1-specific genes (designated as cap 1A-G) and their functions have been preliminarily assigned based on sequence similarities.