SEQUENCE AND EXPRESSION PATTERN OF J-CHAIN IN THE AMPHIBIAN, XENOPUS-LAEVIS

We have determined the cDNA sequence encoding J chain, a polypeptide a ccessory molecule associated with polymeric Ig, from the anuran amphib ian, Xenopus laevis (South African clawed frog). The translated polype ptide consists of 164 amino acid residues, including the signal sequen ce, and is somewhat longer than the corresponding sequence in mouse an d cow, the two mammalian species in which the signal sequence of J cha in has been determined. J chain in several mammalian species (human, m ouse, cow and rabbit) has eight Cys residues. In the human chain, two of these Cys residues, the second and third in the sequence, have been shown to form disulfide bridges to heavy chains in IgM or IgA; the re maining Cys residues form intrachain disulfide bonds. The Xenopus J ch ain contains only seven of these Cys residues. Ser is found at the pos ition corresponding to the third Cys in mammalian J chains. Northern b lot analysis, performed on RNA isolated from various organs of 3-month old frogs, indicated that the highest level of expression was in the intestine. Transcripts corresponding to J chain were also detected in the spleen and at very low levels in the thymus. (C) 1997 Elsevier Sci ence Ltd. All rights reserved.