Friday, February 15, 2008

The BEN domain: A novel module in chromatin function and DNA viruses

The BEN domain is an α helical domain detected in diverse animal transcription factors and chromatin proteins, including BANP/SMAR1, NAC1, Drosophila mod(mdg4) isoform C and the vertebrate sex combs in midleg-like-1. The domain is also found in chordopoxviruses (E5R) and in several polydnavirus proteins and is among the few proteins with a known domain in the latter viruses.

Architectural diversity. The BEN domain is often found in multiple tandem copies. Our analysis suggests that these tandem copy containing proteins arose on multiple occasions independently in evolution. This suggests an inherent property of the domain to form multimeric assemblies. In addition BEN domains are fused to a variety of chromatin associated domains such as POZ, MCAFN, C4DM, C2H2 fingers and SAM, and also to the RNaseT2 domain in polydnaviruses.
Functional predictions. Experimental studies suggest that the BEN domain is involved in protein-protein interactions. However, contextual analysis points to a possible role in DNA binding. This is inferred from the fusion of the BEN domain N-terminal to the C4DM in insects, and by its presence in an isoform of mod(mdg4) and the Broad complex loci in the same exon position as other DNA binding domains.

Viral BEN domains: The chordopoxviral protein E5R, a lateral transfer of the vertebrate KIAA1553, is an abundant early virosome protein, and it may be involved in organizing viral DNA during replication. Interestingly, the Molluscipox virus E5R ortholog appears to be a secondary displacement of the viral E5R by the host KIAA1553. The polydnaviruses have one to many copies of proteins with the BEN domain. Some versions are additionally fused to RNaseT2. This suggests a possible role in RNA processing, or perhaps in modifying host function.
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