Abstract. The myogenin (MYOG) gene fulfills a key function in muscle differentiation by controlling the onset of myoblast fusion and the establishment of myofibers. In meat-producing animals like pigs and cattle, myofiber numbers have been related to growth capacity. We have characterized the porcine MYOG gene to detect genetic variation at this locus and to relate it to growth characteristics. MYOG gene fragments were isolated by PCR on genomic DNA and by screening a genomic library with a mixture of the four human MyoD cDNA fragments. Both the exons and promoter region were very similar to the human and mouse genes. Southern blot analysis of 105 unrelated pigs revealed three polymorphic MspI sites, located in the promoter region, the second intron, and at the 3' side of the gene. PCR-RFLP tests detecting four MYOG alleles were developed. PCR analysis of a panel of pig-rodent somatic cell hybrids confirmed the genetic localization of MYOG on pig Chromosome (Chr) 9. The PCR-RFLP tests and microsatellite markers on Chr 9 offer the possibility to genotype large numbers of pigs for studies of genetic linkage to meat deposition and growth characteristics.

We describe the use of random peptide sequences for the mapping of antigenic determinants. An oligonucleotide with a completely degenerate sequence of 17 or 23 nucleotides was inserted into a bacterial expression vector. This resulted in an expression library producing random hexa- or octapeptides attached to a beta-galactosidase hybrid protein. Mimotopes, or antigenic sequences that mimic an epitope, were selected by immunoscreening of colonies with monoclonal antibodies, which were specific for antigenic sites on the spike protein of the coronavirus transmissible gastroenteritis virus. We report one mimotope for antigenic site II, eight for site III and one for site IV. The site III and site IV mimotopes were closely similar to the corresponding linear epitopes, localized previously in the amino acid sequence of the S protein. An alignment of the site II mimotope and the sequence of the S protein around Trp97, which is substituted in escape mutants, suggests that this mimotope mimics a conformational epitope located around residues 97-103. Applications of mimotopes to epitope mapping, serodiagnosis and vaccine development are discussed.

Porcine-specific polymerase chain reaction (PCR) and a pig-rodent somatic cell hybrid panel were used to map two members of the MyoD gene family. MYOD1 was assigned to pig chromosome 2 and MYF5 to chromosome 5.