title: Unusual chromatin structure associated with monoparalogous transcription of the Babesia bovis ves multigene family.
abstract: Rapid antigenic variation in Babesia bovis involves the variant erythrocyte surface antigen-1 (VESA1), a heterodimeric protein with subunits encoded by two branches of the ves multigene family. The ves1α and ves1β gene pair encoding VESA1a and 1b, respectively, are transcribed in a monoparalogous manner from a single locus of active ves transcription (LAT), just one of many quasi-palindromic ves loci. To determine whether this organization plays a role in transcriptional regulation, chromatin structure was first assessed. Limited treatment of isolated nuclei with micrococcal nuclease to assay nucleosomal patterning revealed a periodicity of 156-159 bp in both bulk chromatin and specific gene coding regions. This pattern also was maintained in the intergenic regions (IGr) of non-transcribed ves genes. In contrast, the LAT IGr adopts a unique pattern, yielding an apparent cluster of five closely-spaced hypersensitive sites flanked by regions of reduced nucleosomal occupancy. ves loci fall into three patterns of overall sensitivity to micrococcal nuclease or DNase I digestion, with only the LAT being consistently very sensitive. Non-transcribed ves genes are inconsistent in their sensitivity to the two enzymatic probes. Non-linear DNA structure in chromatin was investigated to determine whether unique structure arising as a result of the quasi-palindromic nature of the LAT may effect transcriptional control. The in vitro capacity of ves IGr sequences to adopt stable higher-order DNA structure is demonstrated here, but the presence of such structure in vivo was not supported. Based upon these results a working model is proposed for the chromatin structural remodeling responsible for the sequential expression of ves multigene family members from divergently-organized loci.
authors.affiliation: Department of Infectious Diseases and Pathology, University of Florida, Gainesville, FL, USA.
authors.forename: Yingling
authors.initials: Y
authors.lastname: Huang
authors.forename: Yu-Ping
authors.initials: YP
authors.lastname: Xiao
authors.forename: David R
authors.initials: DR
authors.lastname: Allred
mesh_terms: D000818:Animals; D016793:Babesia bovis / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D001404:Babesiosis / Q000469:parasitology / Q000662:veterinary*; D002417:Cattle; D002418:Cattle Diseases / Q000469:parasitology*; D002843:Chromatin / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D005786:Gene Expression Regulation; D005810:Multigene Family; D009690:Nucleic Acid Conformation; D009707:Nucleosomes / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D015800:Protozoan Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D014158:Transcription, Genetic
chemical_list: D002843:Chromatin; D009707:Nucleosomes; D015800:Protozoan Proteins