We apologize for the errors that occurred in the Summary of both the online and print versions of this paper. The corrections are detailed below.In line 1 of the Summary, Schizosaccaromyces pombe is incorrectly referred to as 'Saccharomyces pombe'. Correct version: Fission yeast (Schizosaccaromyces pombe) centromere DNA is organized in a central core region flanked on either side by a region of outer repeat (otr) sequences.In line 29 of the Summary, the word 'of' is missing. Correct version: The declustering of centromeres in mis6 cells correlated with loss of the Ndc80 kinetochore marker protein from the centromeres.In line 35 of the Summary, mis-segregation has been incorrectly changed to 'misaggregation'. Correct version: Time-lapse microscopy of live mis6 and nuf2-1 mutant cells in mitosis showed similar severe mis-segregation phenotypes whereas the rik1 mutants showed a mild cohesion defect. Erratum IntroductionThe centromere in most species can be observed as a localized primary constriction of the metaphase chromosome. Centromeric DNA harbors a large protein complex, the kinetochore, which mediates the attachment of the chromosomes to the mitotic and meiotic spindle thereby ensuring proper chromosome segregation. Although centromeric DNA sequences have little homology between organisms, structurally the centromeres and kinetochores are similar between such distantly related species as Saccharomyces cerevisiae, Schizosaccharomyces pombe, Drosophila melanogaster and humans (reviewed by Blower et al., 2002). Centromeric DNA in fission yeast occupies 40-100 kb on each chromosome, organized with a unique central core sequence (CC/cnt) (Chikashige et al., 1989;Clarke and Baum, 1990) flanked by inner (imr/B) and outer (otr/K+L) repeat arrays (Fig. 1A). The use of chromatin immunoprecipitation (ChIP) has established that the central core region is bound by proteins Cnp1 (fission yeast homologue of human CENP-A) Mis6 and Mis12 bind (Takahashi et al., 2000;Saitoh et al., 1997) and XMAP215 homologues, Dis1 and Mtc1/Alp14 (Garcia et al., 2001;Nakaseko et al., 2001). In contrast the outer repeated region is occupied by the chromodomain proteins Swi6 and Chp1 that are structural components of centromeric heterochromatin over the imr and otr repeats (Partridge et al., 2000). The passenger protein Bir1/Cut17 transiently associates with the imr and otr repeats and not with the central core region in mitosis ). Thus, the DNA sequence analysis that first revealed the symmetrical organization of S. pombe centromeres (Clarke et al., 1986;Chikashige et al., 1989) and the pattern of protein binding (established by ChIP analysis) to the central core and otr/imr regions suggested that the fission yeast centromeres are composed of two different domains. The contrasting phenotypes of mutants such as rik1 and swi6, with defects in heterochromatin Ekwall et al., 1996), as compared to mutants such as mis6, with defects in the central core (Saitoh et al., 1997), indicated that these two domains are functionally distinct. Interphase cen...

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Minisatellites are composed of tandem repetitive DNA sequences and are present at many positions in the human genome. They frequently mutate to new length alleles in the germline, by complex and incompletely understood recombination mechanisms which may operate during meiosis. In several minisatellites the mutation events are restricted to one end of the repeat array, indicating a possible association with elements that act in cis. Mutant alleles do not show exchange of flanking regions. To construct a model system suitable for further investigations of the mutation process, we have integrated the human minisatellite MS32, flanked by synthetic markers, in the vicinity of a meiotic recombination hot spot upstream of the LEU2 locus in the yeast Saccharomyces cerevisiae. Here we provide direct evidence for a meiotic origin of MS32 mutations. Mutation events were polarised towards both ends of the minisatellite and varied from simple duplications and deletions to complex intra- and interallelic events. Interallelic events were frequently accompanied by exchange of regions flanking the minisatellite. The results also support the notion that cis-acting elements are involved in the mutational process. The fact that MS32 mutant structures are similar in yeast and human shows that meiotic recombination plays a crucial role in both organisms and emphasises the usefulness of yeast strains harbouring minisatellites as a model system for the study of minisatellite mutation.

Here we describe the phenotypic characterization of the cta4 + gene, encoding a novel member of the P4 family of P-type ATPases of fission yeast. The cta4Δ mutant is temperature sensitive and cold sensitive lethal and displays several morphological defects in cell polarity and cytokinesis. Microtubules are generally destabilized in cells lacking Cta4p. The microtubule length is decreased, and the number of microtubules per cell is increased. This is concomitant with an increase in the number of microtubule catastrophe events in the midzone of the cell. These defects are likely due to a general imbalance in cation homeostasis. Immunofluorescence microscopy and membrane fractionation experiments revealed that green fluorescent protein–tagged Cta4 localizes to the ER. Fluorescence resonance energy transfer experiments in living cells using the yellow cameleon indicator for Ca2+ indicated that Cta4p regulates the cellular Ca2+ concentration. Thus, our results reveal a link between cation homeostasis and the control of cell shape, microtubule dynamics, and cytokinesis, and appoint Ca2+ as a key ion in controlling these processes.

This is a call for action to scientific journals to introduce reporting requirements for toxicity and ecotoxicity studies. Such reporting requirements will support the use of peer‐reviewed research studies in regulatory decision‐making. Moreover, this could improve the reliability and reproducibility of published studies in general and make better use of the resources spent in research.

Polychlorinated biphenyls (PCBs) are lipophilic compounds, several of which are toxic and carcinogenic. Complex mixtures of PCBs (e.g., Aroclor) have been widely used in the industry. The persistence of PCBs, in combination with poor waste management, has led to a large‐scale distribution of PCBs in the biosphere. The toxic and carcinogenic effects of PCBs are poorly understood, but are suggested to be associated with Ah receptor binding and induction of the Ah‐gene battery. We have previously shown that a higher‐chlorinated PCB mixture, Aroclor 1254, significantly increased the germline mutation rate at the mouse minisatellite PC‐1. We have recently developed an in vitro model system to study and characterize spontaneous and induced meiotic mutations in human minisatellites integrated in yeast. Here, for the first time, we have used this model system to show that chemicals, in this case Aroclor 1254, can induce meiotic length mutations at the human minisatellite MS32 in a yeast strain harboring 38‐ and 42‐repeat‐unit alleles. The results also show that the size distribution of mutant MS32 alleles differs between PCB and the control, with a larger proportion of mutant allele sizes below 29 repeat units in the PCB series. These alleles were not structurally different from the alleles of the same size in the control. We conclude that PCBs induce minisatellite mutations in meiosis and have recombinogenic properties, and that the mutations are induced in an Ah receptor‐independent manner. The induction of minisatellite mutations in meiosis as an indication of genomic damage must be taken into account in the risk assessment of PCBs and other environmental contaminants. Environ. Mol. Mutagen. 34:285–290, 1999. © 1999 Wiley‐Liss, Inc.

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