Fig. 1. (A) Primary structure of the three cDNA-derived cysteine string protein isoforms CSP1, CSP3 and CSP4, and the postulated isoform CSP2*. The conserved `J' domain, the cysteine string region (`CS'), and the epitopes recognized by the three available monoclonal antibodies DCSP1, DCSP2 and DCSP3 are boxed, the amino acids deleted in the mutant proteins L8 and C27 are underlined. (B) Schematic representation of the exon-intron structure of the three known Csp transcripts cDNA-1, cDNA-3 and cDNA-4, and the hypothetical cDNA-2*. The white vertical lines in exons 1, 6* and 7 indicate start and stop codons, which delimit the open reading frames. The approximate molecular masses in SDS gels and the recognition (+) of the four isoforms by the monoclonal antibodies DCSP1, DCSP2 and DCSP3 are indicated. (C) Genomic region of the Csp locus and the extent of the deficiency of the Csp^U1w null mutant compared with wild type (WT). (D) cDNA-1 derived rescue constructs lcDna1 (lcD-1) and scDna1 (scD-1). The constructs consist of genomic fragments of different sizes (compare with C) containing regulatory sequences and exons 1, 2 and part of exon 3, as well as introns 1 and 2, and a common cDNA-1 fragment (hatched) containing the rest of exon 3, and exons 4, 5, 6 and 7. The depicted constructs and their in vitro modified versions (cf. A and E) were cloned into the pW8 P-element vector. Restriction enzymes: A=Asp718, B=BamH I, E=EcoRI, H=HindIII, P=Bsp1407I, S=SalI. (E) Amino acid sequence of the cysteine string region of Drosophila CSP and the cysteine string mutant proteins `short cysteine string protein' (SCSP), `cysteine string-less protein' (CSLP), `serine string protein' (SSP) and `cysteine-less protein' (CLP). Cysteine residues (C) are shown in bold.