During B cell development, long-distance DNA interactions are needed for V(D)J 
somatic rearrangement of the immunoglobulin (Ig) loci to produce functional Ig 
genes, and for class switch recombination (CSR) needed for antibody maturation. 
The tissue-specificity and developmental timing of these mechanisms is a subject 
of active investigation. A small number of factors are implicated in controlling 
Ig locus long-distance interactions including Pax5, Yin Yang 1 (YY1), EZH2, 
IKAROS, CTCF, cohesin, and condensin proteins. Here we will focus on the role 
of YY1 in controlling these mechanisms. YY1 is a multifunctional transcription 
factor involved in transcriptional activation and repression, X chromosome 
inactivation, Polycomb Group (PcG) protein DNA recruitment, and recruitment of 
proteins required for epigenetic modifications (acetylation, deacetylation, 
methylation, ubiquitination, sumoylation, etc.). YY1 conditional knock-out 
indicated that YY1 is required for B cell development, at least in part, by 
controlling long-distance DNA interactions at the immunoglobulin heavy chain and 
Igκ loci. Our recent data show that YY1 is also required for CSR. The mechanisms 
implicated in YY1 control of long-distance DNA interactions include controlling 
non-coding antisense RNA transcripts, recruitment of PcG proteins to DNA, and 
interaction with complexes involved in long-distance DNA interactions including 
the cohesin and condensin complexes. Though common rearrangement mechanisms 
operate at all Ig loci, their distinct temporal activation along with the 
ubiquitous nature of YY1 poses challenges for determining the specific 
mechanisms of YY1 function in these processes, and their regulation at the 
tissue-specific and B cell stage-specific level. The large numbers of 
post-translational modifications that control YY1 functions are possible 
candidates for regulation.