CELLULAR AND STRUCTURAL STUDIES OF MYELOMA MUTANTS

My research program has focused on the DNA sequences that mediate
antibody gene rearrangement events, especially heavy (H) chain class
switch recombination. Through examination of the MPCll mouse myeloma
cell line and its variants, we have observed another recombination
event, not confined to antibody genes, namely, unequal sister chroinatid
exchange (USCE). We propose to generate a universal substrate for
assaying recombinogenic sequences, including those that mediate H chain
class switching and those involved in USCE. The MPCll USCE event
involves TC and TG dinucleotide tracts, each of which is capable of
adopting an unusual DNA conformation for TC, a triplestranded structure,
and for TG, left-handed DNA. We propose to examine the DNA conformation
of the juxtaposed TC and TG dinucleotide tracts at the site of the USCE
event. We have begun analysis of MPCll variant cells that are apparently
and interestingly unstable in that they show rearrangements of both
constant and Variable regions, implying some independence from feedback
regulation. Initial study of one variant has led to the observation that
sequences lying 3' of the Ca gene undergo rearrangements in several
myeloma and hybridoma cell lines. We propose experiments to investigate
the functional and structural significance of these 3'beta rearrangement
events to the organization and expression of the Ig cluster. Our long
term goal is to understand how patterned Ig rearrangements may be
governed and how promiscuous rearrangements underlying various
malignancies may be avoided.