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A new frog integumentary mucin (FIM-C.1) has been discovered by molecular cloning. This mucin contains at least six typical P-domains as cysteine-rich modules. Shuffled P-domains have previously been detected in FIM-A.1, and they also form the basis of various P-domain peptides, which presumably have growth-modulating activities. Furthermore, FIM-C.1 contains at least three threonine-rich clusters, which consist of semi-repetitive cassettes. Various polydisperse transcripts have been characterized. They originate from two genes only and differ by deletions/insertions that are congruent with the semi-repetitive cassettes. Thus, polydispersities are probably generated by alternative splicing. Southern analysis revealed genetic polymorphism between different individuals. Furthermore, a specific antiserum was generated against a synthetic peptide deduced from the COOH-terminal end of FIM-C.1 and used for Western analysis.
FIG. 1. Schematic representation of the FIM-C.1 cDNA clones analyzed. A, in the COOH-terminal portion of FIM-C.1, the six Px-domains are hatched and the threonine-rich clusters are designated I, II and Ill. The synthetic oligonucleotides from the SPL and XSP series are denoted S and X, respectively. H, HindIII; P, PstI; X, XbaI. B, localization of the various cDNA clones and their deletions.
FIG.2. Nucleotide sequence and predicted amino acid sequence of the COOH-terminal part of FIM- C.1 This sequence was compiled from t h e cDNA clones listed in Table I, which were all obtained from a single individ- ual. In pFIM.C-5'-1.2, the A a t position 1245 is changed to G (T+ A mutation on aminoacidlevel);inpF1M.C-5'-11.13 position 828 is changed to G (K- - f E mutation), whereas in pF1M.C-P21-1 position 1062 isaltered to C (C + R mutation). Triangles flank a deletion in pFIM.C-5'-10.11, which corresponds precisely tothe second P-domain (P2). The 22 semi-repetitive cassettes in clus- ters1-111(seealsoFig.6) areunderlined. Deletions (A) of single cassettescause the polydisperse nature of the cDNA clones: pFIM.C-5'-1.7 ( A 17a-20b), pFIM.C-5'-10.8 ( A 12, 14a, 14b), pFIM.C-5'-10.11 (A 11,12, PI; 14a lacks
a single threonine codon), pF1M.C-P21- 1 (A 11,12,14a, 14b),pF1M.C-P21-2 (A 12).The conserved tryptophan residue of each P-domain andthe equivalent histidine residue in PI are encircled. Also markedare restrictionsites, the posi- tions of the synthetic oligonucleotides, and the polyadenylation signal. The se- quenceselectedforthe syntheticpeptide (SKP-1) is indicated by a dotted line.
