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ABSTRACTThe choice of adequate methods for epidemiological purposes remains a challenging problem in Neisseria gonorrhoeaemolecular monitoring. In this study, the collection of geographically unrelated gonococci (n= 103) isolated in Russian clinics was comparably tested by (i) a traditional serotyping scheme, (ii) portyping, (iii) Neisseria gonorrhoeaemultiantigen sequence typing (NG-MAST), and (iv) multilocus sequence typing (MLST). It is shown that, according to sequencing data, a third of the strains carried new porB1alleles, as well as tbpBones, and more than half of the samples had new sequence types (STs) as determined by NG-MAST or MLST. The discriminatory power for each typing method was calculated by using the Hunter-Gaston discriminatory index, D. Commonly, modern nucleic acid-based typing methods (portyping, NG-MAST, and MLST) appeared to be more efficient than the classical serotyping scheme. While the traditional serotyping gave a Dvalue of 0.82, the portyping, NG-MAST, and MLST approaches yielded Dvalues of 0.97, 0.98, and 0.91, respectively. Each typing technique revealed the distribution of gonococci slightly correlated with their geographical sources. However, only the MLST method STs were highly associated with certain phenotypes. Although ST1594, ST1892, and ST6720 were typical for susceptible gonococci, ST1901 and ST6716 were undoubtedly associated with a multidrug-resistant phenotype. We conclude that every tested nucleic acid-based typing method is suitable for N. gonorrhoeaemolecular surveillance. However, the MLST method seems to serve large-scale epidemiological purposes, whereas the NG-MAST and portyping approaches are more appropriate for the investigation of local outbreaks.

Centromeric region of human chromosome 21 comprises two long alphoid DNA arrays: the well homogenized and CENP-B box-rich α21-I and the α21-II, containing a set of less homogenized and CENP-B box-poor subfamilies located closer to the short arm of the chromosome. Continuous alphoid fragment of 100 monomers bordering the non-satellite sequences in human chromosome 21 was mapped to the pericentromeric short arm region by fluorescence in situ hybridization (α21-II locus). The alphoid sequence contained several rearrangements including five large deletions within monomers and insertions of three truncated L1 elements. No binding sites for centromeric protein CENP-B were found. We analyzed sequences with alphoid/non-alphoid junctions selectively screened from current databases and revealed various rearrangements disrupting the regular tandem alphoid structure, namely, deletions, duplications, inversions, expansions of short oligonucleotide motifs and insertions of different dispersed elements. The detailed analysis of more than 1100 alphoid monomers from junction regions showed that the vast majority of structural alterations and joinings with non-alphoid DNAs occur in alpha satellite families lacking CENP-B boxes. Most analyzed events were found in sequences located toward the edges of the centromeric alphoid arrays. Different dispersed elements were inserted into alphoid DNA at kinkable dinucleotides (TG, CA or TA) situated between pyrimidine/purine tracks. DNA rearrangements resulting from different processes such as recombination and replication occur at kinkable DNA sites alike insertions but irrespectively of the occurrence of pyrimidine/purine tracks. It seems that kinkable dinucleotides TG, CA and TA are part of recognition signals for many proteins involved in recombination, replication, and insertional events. Alphoid DNA is a good model for studying these processes.

It can be invoked from the theory of tandem repeat homogenization that DNA on a satellite/non‐satellite border may carry sequence marks of molecular processes basic to satellite evolution. We have sequenced a continuous 17‐kb alpha satellite fragment bordering the non‐satellite in human chromosome 21, which is devoid of higher‐order repeated structure, contains multiple rearrangements, and exhibits higher divergence of monomers towards the border, indicating the lack of efficient homogenization. Remarkably, monomers have been found with mutually supplementary deletions matching each other as reciprocal products of unequal recombination, which provide evidence for unequal cross‐over as a mechanism generating deletions in satellite DNA.