Showing papers by "Susumu Tonegawa published in 1982"

Organization, structure, and assembly of immunoglobulin heavy chain diversity DNA segments.

Abstract: We have identified, cloned, and sequenced eight different DNA segments encoding the diversity (D) regions of mouse immunoglobulin heavy-chain genes. Like the two D segments previously characterized (16, 17), all eight D segments are flanked by characteristic heptamers and nonamers separated by 12-bp spacers. These 10 D segments, and several more D segments identified but not yet sequenced, can be classified into three families based on the extent of sequence homology. The SP2 family consists of nine highly homologous D segments that are all 17-bp long and clustered in a chromosomal region of approximately 60 kb. The FL16 family consists of up to four D segments, two of which were mapped in the 5' end region of the SP2-D cluster. The two FL16D segments are 23 and 17 bp long. The third, the Q52 family, is a single-member family of the 10-bp-long DQ52, located 700 bp 5' to the JH cluster. We argue that the D-region sequences of the majority of heavy chain genes arise from these germline D segments by various somatic mechanisms, including joining of multiple D segments. We present a specific model of D-D joining that does not violate the 12/23-bp spacer rule.

DNA sequences of the joining regions of mouse lambda light chain immunoglobulin genes

Abstract: The joining (J) segments of mouse immunoglobulin lambda light chain genes, lambda 2, lambda 3, and a presumptive lambda 4, were cloned, and their sequences were determined and compared with that of lambda 1. Although all the lambda J segments share sequence homology, the J1 and J4 segments and the J2 and J3 segments, respectively, are more homologous. These sequence data, together with the fact that present day lambda genes occur in two clusters, 5' J3C3J1C1 3' and 5' J2C2J4C4 3', further substantiates a probable evolutionary duplication unit, JIICIIJICI, with II the precursor of lambda 3 and lambda 2 and I the precursor of lambda I and lambda 4. From the J4 sequence, we conclude that the lambda 4 gene is most likely nonfunctional (i.e., a pseudogene). The signal nonamer sequence 5' to J3 differs from that of J1 in two consecutive base pairs. This difference could account in part for the lower level of expression of lambda 3 as compared with lambda 1 in mouse serum.

ORGANIZATION AND EXPRESSION OF MOUSE λ LIGHT CHAIN IMMUNOGLOBULIN GENES

Abstract: The four λ light chain constant region (C) genes have been cloned from BALB/c mouse embryo DNA. The Cλ 1 gene segment was previously analyzed (1,2). Each Cλ gene carries its own J segment approximately 1.3 kilobases to its 5′ side which contrasts with both the kappa (K) and heavy (H) chain immunoglobulin gene systems with a cluster of four functional joining (J) sequences 5′ to the constant gene segment(s). The four Cλ genes occur in two clusters: 5′J 3 C 3 J 1 C 1 3′ and 5′J 2 C 2 J 4 C 4 3′. The J DNA segments of λ 2 , λ 3 and λ 4 were sequenced and compared with that of λ 1 . Sequence homology (particularly in the non-coding regions) was greatest between J 1 and J 4 and between J 2 and J 3 which suggests, along with the similar organization of JCJC and crosshybridization of C 1 and C 4 and of C 2 and C 3 , that the two clusters are products of a duplication event. A single variable region (V)λ gene, 5′ of each JCJC cluster, was probably part of this duplication unit. We have confirmed that there are only two Vλ genes in mouse (Vλ 1 and Vλ 2 ), and we have also shown that the Vλ 1 gene segment is joined productively to Cλ 3 in a λ 3 myeloma. Vλ 1 has been found associated only with Cλ 3 or Cλ 1 and in most cases Vλ 2 joins with Cλ 2 (the exceptions allow us to deduce a probable organization of the total λ locus). From these data and from the analysis of germ line and rearranged Vλ genes in myelomas, the two Vλ genes must be interspersed by a JCJC cluster if the looping-out and deletion model is generally used for V-J joining. The organization of the λ locus is most likely: 5′V 2 -J 2 C 2 J 4 C 4 -V 1 -J 3 C 3 J 1 C 1 3′. The λ 4 gene is probably not functional since the J 4 sequence does not contain a valid splice site and has a 2-bp deletion in the signal heptamer sequence 5′ to J 4 . The signal nonamer sequence 5′ to J 3 differs from that of J 1 in two consecutive base pairs and may account for the lower level of λ expression as compared with λ 1 in mouse lymphocytes.