V. Dufour et F. Nau, GENOMIC ORGANIZATION OF THE SHEEP IMMUNOGLOBULIN JH SEGMENTS AND THEIR CONTRIBUTION TO HEAVY-CHAIN VARIABLE REGION DIVERSITY, Immunogenetics, 46(4), 1997, pp. 283-292
The sheep immunoglobulin heavy chain Igh-J locus has been characterize
d in order to determine the genomic organization of JH segments and th
eir contribution to heavy chain diversity. The locus contains six segm
ents, of which two are functional and four are apparently pseudogenes.
These segments span a 1.8 kilobase (kb) region. The distance between
JH-ps4 (the 3'-most segment) and the first domain of the CI-chain enco
ding constant gene is about 5 kb. The two functional JH segments have
a standard upstream recombination signal sequence, including heptamer
and nonamer sequences separated by a 22-23 nucleotide spacer, and end
with a RNA donor splice site. These two segments possess all the chara
cteristic JH invariant residues and are found in expressed Ct heavy ch
ain variable regions. The 5' functional JH1 segment is used in more th
an 90% of the cDNAs sequenced to date. The contribution of JH segment
germline multiplicity to variable regions diversity appears therefore
to be minimal. Comparison with other mammalian JH segments shows that
all loci are very closely related and probably have evolved from a com
mon ancestral locus.