The role of components of recombination signal sequences in immunoglobulingene segment usage: a V81x model

It has long been appreciated that some immunoglobulin (and T-cell receptor) gene segments are used much more frequently than others. The V-H Segment V 81x is a particularly striking case of overusage, Its usage varies with the stage of B-cell development and with the strain of mice, but it is always high in B cell progenitors. We have found that the coding sequence and the recombination signal sequences (RSS) are identical in five mouse strains, i ncluding CAST/Ei, a strain derived from the species Mus castaneus, Thus, th e strain differences cannot be attributed to sequences within V81x itself. V81x RSS mediated recombination at rates significantly higher than another V-H RSS, Although the V81x nonamer differs at one base pair from the consen sus sequence, an RSS with this nonamer and a consensus heptamer recombines as well as the consensus RSS. When the V81x spacer is replaced by that of V A1, the frequency of recombination decreases by similar to 5-fold; thus, th e contribution of variation in natural spacers to variability in V-H usage in vivo is likely to be more than has been previously appreciated, Furtherm ore, the contribution of the heptamer and nonamer to differential V-H usage in our assay is correlated inversely with their conservation throughout th e V-H locus.