| In the TCR Beta locus, variable (V), diversity (D), and joining (J) gene segments assemble by a process known as V(D)J recombination. Assembly in the TCR Beta locus is ordered, with D Beta to J Beta rearrangement occurring on both alleles before V Beta to D Beta rearrangement. Recombination occurs following a restriction known as the 12/23 rule, such that gene segments flanked by Recombination Signal Sequences (RSSs) with a dissimilar number of spacer nucleotides (12 or 23) are capable of rearranging. In the TCR Beta locus, V Beta gene segments are flanked by a 3' 23-RSS, the D Beta gene segments are flanked with a 5' 12-RSS and a 3 ' 23-RSS, and the J Beta gene segments are flanked by 5 ' 12-RSSs. Although the 12/23 rule would be fulfilled by direct targeting of V Beta rearrangement to the J Beta gene segments, most TCR Beta chain sequences contain D Beta nucleotides, suggesting contribution of the D Beta gene segment is important for the normal generation of TCR Beta chains.;Our studies have elucidated the requirement for the RSS directly 5 ' of the D Beta 1 gene segment for targeting V Beta rearrangement, enforcing a novel constraint on gene rearrangement in the TCR Beta locus beyond 12/23 restriction. We have demonstrated this mechanism is necessary for preserving D Beta gene segment utilization in order to generate a diverse population of TCR Beta chains with a normal CDR3 distribution. In addition, we show here that the 5' D Beta RSS heptamer and nonamer, and spacer, are required for the efficient targeting of V Beta rearrangement, as well as other nucleotides conserved between the 5' D Beta and 5' D Delta RSSs. Finally, experiments have focused on further examining the association of a functional TATA box spanning the nonamer and spacer of the 5'D Beta 1 RSS with the targeting of V Beta gene segment rearrangement. |
