Structural heterogeneity of the emm gene cluster in group A streptococci.

One or more distinct copies of emm genes lie within a gene cluster that is located downstream from a transcriptional regulatory gene (mry). Mry is a positive regulator for the genes in this cluster and for the downstream gene, scpA. The objective of this study is to examine the structure of this cluster and the distribution of specific alleles within the cluster among group A streptococcal isolates of 32 different serotypes. The peptidoglycan (PG)-spanning domain, which exists in four divergent forms, was used to identify specific alleles of the genes within the emm cluster. Gene content of the cluster was determined by Southern hybridization with allele-specific oligonucleotides. Five different chromosomal patterns for this cluster were observed. Sequence heterogeneity in the adjacent mry locus was demonstrated by the ability of some of the isolates to hybridize with a whole mry gene probe, but not with mry-based oligonucleotide probes. A PCR-based chromosomal mapping technique was used to examine further the gene order within the emm gene clusters. Structural heterogeneity of the emm gene cluster was found within class I isolates in this study, while class II isolates were relatively homogeneous at this chromosomal locus and distinct from class I.

Somatic embryogenesis from three commercially important inbreds of Zea mays.

Zea mays (maize) genotypes B73, Mo17 and LH38 were evaluated for their capacity to undergo somatic embryogenesis. Over 1500 immature embryos (ie's) of B73, 2900 ie's of LH38 and 400 ie's of Mo17 were excised 10-17 days after pollination and plated on six different media. Overall response, reported as a percentage of the ie's plated that developed embryogenic callus, was 2.1%, 1.6% and 26% for LH38, B73 and Mo17, respectively. Best response on a given medium for each of these genotypes was 9.2% (LH38), 4.4% (B73) and 100% (Mo17). Other parameters examined for their effects on production of embryogenic callus included self vs. sib pollination, ear ranking (1st, 2nd or 3rd ear), and temperature shock, all of which had no significant effect. Plantlets regenerated from selected treatments of B73 have been grown to maturity, selfed or sibbed and seed collected for field evaluation.

Molecular evolution of a multigene family in group A streptococci.

The emm genes are members of a gene family in group A streptococci (GAS) that encode for antiphagocytic cell-surface proteins and/or immunoglobulin-binding proteins. Previously sequenced genes in this family have been named "emm," "fcrA," "enn," "arp," "protH," and "mrp"; herein they will be referred to as the "emm gene family." The genes in the emm family are located in a cluster occupying 3-6 kb between the genes mry and scpA on the chromosome of Streptococcus pyogenes. Most GAS strains contain one to three tandemly arranged copies of emm-family genes in the cluster, but the alleles within the cluster vary among different strains. Phylogenetic analysis of the conserved sequences at the 3' end of these genes differentiates all known members of this family into four evolutionarily distinct emm subfamilies. As a starting point to analyze how the different subfamilies are related evolutionarily, the structure of the emm chromosomal region was mapped in a number of diverse GAS strains by using subfamily-specific primers in the polymerase chain reaction. Nine distinct chromosomal patterns of the genes in the emm gene cluster were found. These nine chromosomal patterns support a model for the evolution of the emm gene family in which gene duplication followed by sequence divergence resulted in the generation of four major-gene subfamilies in this locus.

Genetic correlates of throat and skin isolates of group A streptococci.

The existence of discrete populations of throat and skin strains of group A streptococci has long been recognized; however, a molecular basis for this distinction is not known. The emm gene structure was analyzed for 105 isolates obtained from patients with well-defined group A streptococcal diseases: uncomplicated pharyngitis, impetigo, and acute rheumatic fever. Four emm gene sub-family forms, defined by nucleotide sequence differences in regions encoding the peptidoglycan-spanning domain of M and M-like surface proteins, were found to exist in five different chromosomal patterns among naturally occurring isolates. Strong correlations were made between disease and the number and arrangement of emm subfamily genes. These findings provide a genetic basis for the historical references to "throat," "skin," and "rheumatogenic" types.