Infection with group A streptococci can result in acute and post-infectious pathology, including rheumatic fever and rheumatic heart disease. These diseases are associated with poverty and are increasing in incidence, particularly in developing countries and amongst indigenous populations, such as Australia's Aboriginal population, who suffer the highest incidence worldwide. Immunity to group A streptococci is mediated by antibodies against the M protein, a coiled-coil alpha helical surface protein of the bacterium. Vaccine development faces two substantial obstacles. Although opsonic antibodies directed against the N terminus of the protein are mostly responsible for serotypic immunity, more than 100 serotypes exist. Furthermore, whereas the pathogenesis of rheumatic fever is not well understood, increasing evidence indicates an autoimmune process. To develop a suitable vaccine candidate, we first identified a minimum, helical, non-host-cross-reactive peptide from the conserved C-terminal half of the protein and displayed this within a non-M-protein peptide sequence designed to maintain helical folding and antigenicity, J14 (refs. 8,9). As this region of the M protein is identical in only 70% of group A streptococci isolates, the optimal candidate might consist of the conserved determinant with common N-terminal sequences found in communities with endemic group A streptococci. We linked seven serotypic peptides with J14 using a new chemistry technique that enables the immunogen to display all the individual peptides pendant from an alkane backbone. This construct demonstrated excellent immunogenicity and protection in mice.

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We have developed a new procedure (Vir typing) for typing Streptococcus pyogenes, by amplifying the entire $to 7-kb variable vir regulon by long PCR. The amplified DNA is then cleaved with Haelll and visualized by ethidlum bromide fluorescence after agarose gel electrophoresis. A simple procedure for preparing DNA of sufficiently high quality from 96 samples was employed simultaneously. This DNA was also used to develop a random amplified polymorphic DNA (RAPD) procedure. The discriminatory power of the two DNA-based procedures was compared with previous methods, M typing, and multilocus enzyme electrophoresis. Both procedures were highly discriminatory, but the stoichiometric yield of restriction fragments in Vir typing allows unambiguous interpretation of results.

Determination of sequences from the nine regions separating the large genes in the 19‐kbp mitochondrial DNA from Torulopsis glabrata has led to the identification of 23 tRNA genes and to the recognition of two types of short repeated sequence implicated in mitochondrial genome expression. The two short repeated sequences are a nonanucleotide motif, 5′‐TATAAGTAA‐3′ and a dodecanucleotide motif, 5′‐TATAATATTCTT‐3′. By RNA sequence determination it has been found that primary transcripts of the small and large rRNAs commence at the 3′ penultimate adenine of the nonanucleotide sequence. This motif has also been found in the DNA sequence upstream from f‐methionine, phenylalanine, leucine, tyrosine and glycine tRNAs, cytochrome oxidase subunit 2 and ATPase subunit 9. The dodecanucleotide sequence is found at least once in each of the nine regions between the large genes. Determination of the 3′ ends of the small and large rRNAs has shown their location to be 8 and 23 nucleotides downstream from the dodecanucleotide sequence. This motif is thought to be involved in signalling processing of polycistronic transcripts. Such transcripts are invoked to account for the production of mRNAs for cytochrome b, cytochrome oxidase subunits 1 and 3, and the joint mRNA for ATPase subunits 8 and 6 genes that lack an adjacent upstream nonanucleotide transcription initiation signal sequence. Processing of polycistronic transcripts at tRNA sequences is also implicated in the formation of mature mRNAs. From the position of tRNA genes relative to the nonanucleotide motif it appears that clusters of these genes are co‐transcribed with downstream sequences for cytochrome oxidase subunits 1 and 3.

By sequencing a total of 2089 bp of the 16s rRNA and phoE genes it was demonstrated that Calymmatobacterium grandomatis (the causative organism of donovanosis) shows a high level of identity with Klebsiella species pathogenic to humans (Klebsiella pneumoniae, Klebsiella rhinoscleromatis). It is proposed that C. grandomatis should be reclassified as Klebsiella granulomatis comb. nov. An emended description of the genus Klebsiella is given.

The sequential action of X exonuclease and polynucleotide ligase upon redundant joint molecules is sufficient to produce intact polynucleotide chains and heat-stable, biologically active molecules of X DNA, whereas the action of ligase alone is insufficient. These results (a) confirm the previously described mechanism of single-strand assimilation, including a subsidiary mechanism by which the further action of X exonuclease is arrested when a redundant strand is completely assimilated, and (b) represent a simulation of the steps in genetic recombination that follow the formation of biparental complexes (synapsis). X exonuclease is postulated to catalyze a concerted reaction that includes exposure of complementary sequences, formation of heteroduplex regions, and elimination of redundant branches.In a recent report (1) we have shown that X exonuclease can participate in the splicing of two DNA molecules by digesting one strand of a duplex while a single strand from a homologous 1)NA molecule is assimilated in place of the excised nucleotides (Fig. la). In this paper we show that X exonuclease makes a perfect splice: the enzyme stops when the homologous strand is completely assimilated. Without further chemical modification, the interrupted strands of the spliced molecule can be made into intact polynucleotide chains by polynucleotide ligase. This enzymic mechanism, which is called single-strand assimilation, provides new insight into the molecular basis of genetic recombination. METHODS Terminology

Group A streptococcal infections among the Aboriginal communities of the Northern Territory of Australia are endemic, with a concurrently high rate of the postinfection sequelae of rheumatic fever and acute poststreptococcal glomerulonephritis. The majority of the group A streptococcal isolates from the Northern Territory are not typeable by M typing. We recently developed a novel genotyping method, Vir typing. A preliminary study using this method discriminated all the M-nontypeable (MNT) isolates. Vir typing is based on restriction fragment length polymorphisms of the 4-to 7-kb Vir regulon of group A streptococci, which contains a number of genes, including emm (the gene for M protein). A total of 407 isolates of group A streptococci obtained from four Aboriginal communities over a 4-year period were typed by this genotyping method. Forty-two distinct genotypes were found among the isolates, including 22 among the MNT isolates. The correlation between Vir type and M type was good. This genotyping method allows the characterization of all group A streptococcal isolates from Aboriginal communities in the Northern Territory. We also propose that Vir typing be used in conjunction with M typing for epidemiological surveillance in geographical regions where the majority of isolates are MNT. Streptococcus pyogenes, which constitutes the Lancefield group A streptococci (GAS), is the major causative agent of a number of human diseases, ranging from relatively benign conditions, such as pyoderma, to severe invasive diseases, such as toxic shock-like syndrome and necrotizing fasciitis (4). A resurgence of invasive group A streptococcal disease and the postinfection sequela of rheumatic fever in developed countries was reported in the 1980s (11, 16, 36). This resurgence prompted a renewed interest in GAS and its disease manifestations. GAS infections in Aboriginal communities of the Top End of northern Australia are endemic, with up to 70% of children having impetigo, due in part to infection of scabies lesions. The reported rates of acute rheumatic fever and rheumatic heart disease are some of the highest reported anywhere in the world (9, 23). The annual rate of acute rheumatic fever is 2.5 per 1,000 Aboriginal children, and the prevalence rate of rheumatic heart disease is 10.4 per 1,000 Aboriginal people (7). Epidemics of acute post-streptococcal glomerulonephritis (APSGN) occur frequently throughout Aboriginal communities in tropical Australia (13, 34). APSGN was diagnosed in 10% of the Aboriginal children in one community in an APSGN epidemic (34), and it is believed that APSGN is also endemic in the Aboriginal communities. Until recently, M protein serotyping (M typing) has been used extensively in an effort to understand the epidemiology of GAS infections in Aboriginal communities. The antiphagocytic M protein, encoded by the emm gene, is the major virulence factor of GAS, and the antigenic variation of this protein is the basis for the serological typing method. Currently, there are at least 74 characterized M ser...

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