Browsing by Subject "Frameshift Mutation"
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Item Open Access Multiple, conserved cryptic recombination signals in VH gene segments: detection of cleavage products only in pro B cells.(J Exp Med, 2007-12-24) Davila, Marco; Liu, Feifei; Cowell, Lindsay G; Lieberman, Anne E; Heikamp, Emily; Patel, Anjali; Kelsoe, GarnettReceptor editing is believed to play the major role in purging newly formed B cell compartments of autoreactivity by the induction of secondary V(D)J rearrangements. In the process of immunoglobulin heavy (H) chain editing, these secondary rearrangements are mediated by direct V(H)-to-J(H) joining or cryptic recombination signals (cRSs) within V(H) gene segments. Using a statistical model of RS, we have identified potential cRSs within V(H) gene segments at conserved sites flanking complementarity-determining regions 1 and 2. These cRSs are active in extrachromosomal recombination assays and cleaved during normal B cell development. Cleavage of multiple V(H) cRSs was observed in the bone marrow of C57BL/6 and RAG2:GFP and microMT congenic animals, and we determined that cRS cleavage efficiencies are 30-50-fold lower than a physiological RS. cRS signal ends are abundant in pro-B cells, including those recovered from microMT mice, but undetectable in pre- or immature B cells. Thus, V(H) cRS cleavage regularly occurs before the generation of functional preBCR and BCR. Conservation of cRSs distal from the 3' end of V(H) gene segments suggests a function for these cryptic signals other than V(H) gene replacement.Item Open Access Unprecedented loss of ammonia assimilation capability in a urease-encoding bacterial mutualist.(BMC Genomics, 2010-12-02) Williams, Laura E; Wernegreen, Jennifer JBACKGROUND: Blochmannia are obligately intracellular bacterial mutualists of ants of the tribe Camponotini. Blochmannia perform key nutritional functions for the host, including synthesis of several essential amino acids. We used Illumina technology to sequence the genome of Blochmannia associated with Camponotus vafer. RESULTS: Although Blochmannia vafer retains many nutritional functions, it is missing glutamine synthetase (glnA), a component of the nitrogen recycling pathway encoded by the previously sequenced B. floridanus and B. pennsylvanicus. With the exception of Ureaplasma, B. vafer is the only sequenced bacterium to date that encodes urease but lacks the ability to assimilate ammonia into glutamine or glutamate. Loss of glnA occurred in a deletion hotspot near the putative replication origin. Overall, compared to the likely gene set of their common ancestor, 31 genes are missing or eroded in B. vafer, compared to 28 in B. floridanus and four in B. pennsylvanicus. Three genes (queA, visC and yggS) show convergent loss or erosion, suggesting relaxed selection for their functions. Eight B. vafer genes contain frameshifts in homopolymeric tracts that may be corrected by transcriptional slippage. Two of these encode DNA replication proteins: dnaX, which we infer is also frameshifted in B. floridanus, and dnaG. CONCLUSIONS: Comparing the B. vafer genome with B. pennsylvanicus and B. floridanus refines the core genes shared within the mutualist group, thereby clarifying functions required across ant host species. This third genome also allows us to track gene loss and erosion in a phylogenetic context to more fully understand processes of genome reduction.