Unusual chromatin structure associated with monoparalogous transcription of the Babesia bovis ves multigene family

作者：Huang Yingling; Xiao Yu Ping; Allred David R^*

来源：International Journal for Parasitology, 2013, 43(2): 163-172.

DOI：10.1016/j.ijpara.2012.10.018

• Antigenic variation
• Babesia bovis
• Chromatin remodeling
• Chromatin structure
• Nucleosome remodeling
• Promoter structure
• Transcription

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 ves1 alpha and ves1 beta gene pair encoding VESA1a and 1b, respectively, are transcribed in a monoparalogous manner from a single locus of active yes transcription (LAT), just one of many quasi-palindromic yes 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 yes 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. yes 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 yes 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 yes 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 yes multigene family members from divergently-organized loci.

• 出版日期2013-2