The mei4؉ gene of the fission yeast Schizosaccharomyces pombe was cloned by functional complementation. The mei4 disruptant failed to complete meiosis-I but could proliferate normally. Meiosis is required for the formation of germ cells which transmit genetic information from generation to generation. This specialized nuclear division is characterized by a reduction in the chromosome number and frequent genetic recombination, both of which have contributed to the evolution of eukaryotes. Although meiosis has basically the same machinery, including spindles, centrosomes, and kinetochores, as mitosis in somatic cells, these two nuclear divisions are different in many aspects. Meiosis-specific gene products must be responsible for the various different features of meiosis, especially those of meiosis-I, such as the synapsis of homologous chromosomes, nondisjunction of sister chromatids, crossing over, and chiasmata formation.

Spatial and temporal variation in Microcystis species composition and microcystin concentration, quantified by enzyme-linked immunosorbent assay and high-performance liquid chromatography, were investigated during a 3-year period (1998-2000) in the Northern Basin of Lake Biwa. The Northern Basin generally had a concentration of 5 microg L(-1) or less, except at station 1 (Nagahama Bay) from July to October during the study period. The maximum concentration at station 1 was 22.7, 35.9, and 22.0 microg L(-1) in October of 1998, 1999, and 2000, respectively. Eleven species of cyanobacteria were observed: Microcystis aeruginosa, M. ichthyoblabe, M. novacekii, M. wesenbergii, Oscillatoria raciborskii, Anabaena oumiana, A. affinis, A. flos-aquae, A. ucrainica, A. smithii, and A. crassa. Of these, M. aeruginosa and M. wesenbergii were the main components observed. A high concentration of microcystin in the lake water was mostly a result of variation in the relative amount of toxic M. aeruginosa rather than of the total Microcystis cell number. This was supported by the analytical results for isolated strains. Microcystis spp. cell density in the Northern Basin appeared to increase gradually over the course of the study. This is the first study to have surveyed the Northern Basin of Lake Biwa, which supplies drinking water to 14 million people and is the largest lake in Japan.

We have isolated a hybrid plasmid, pDB(mei2)2, containing a 7.4-kilobases (kb) DNA fragment from a Schizosaccharomyces pombe genomic library which is able to complement the mei2 mutation of S. pombe. Integration of the cloned DNA sequence at the mei2 site on chromosome I demonstrated that it contained the mei2 gene. This gene was localized on a 4.7-kb HindIl-Pvull fragment in the subclone pFMV402. Transcriptional regulation was studied by Northern blot analysis in which polyadenylated RNA was prepared from a heterozygous (h+N/h-s) diploid strain cultured either in nitrogen-rich growth medium or in nitrogen-free sporulation medium. The size of the major mei2 mRNA, which always gave a broad band, was estimated to be 4.2 ± 0.2 kb, and a few minor bands (e.g., 3.2 and 1.8 kb) appeared as well. These transcripts appeared more abundantly in sporulating cells than in growing cells. Neither the mating type genes (mat) nor the mei3 gene was essential for transcription of the mei2 gene, since ample mei2 mRNA was detected in sporulation-deficient cells transferred to sporulation medium, such as h+N/h+N and h-s/h-s homozygotes, as well as meil and mei3 mutants.Nutritional starvation is one of the major signals for sexual reproduction in a wide range of organisms. In the fission yeast Schizosaccharomyces pombe, sexual processes (mating in haploids and meiosis in diploids) are induced by the depletion of a nitrogen source from the culture medium (8, 9).Heterozygosity at the mating type locus (mat) is another prerequisite for the initiation of meiosis, implying that both matl-P and matl-M products are required for this process (9). In addition to the mat genes, two additional genes, mei2 and mei3, are involved in the initial step of meiosis as positive regulators (5, 16).Recently, Iino and Yamamoto (11,12) and Nurse (15) have isolated a conditional mutant, pati or rani, which is able to undergo meiosis at the restrictive temperature even in the presence of a nitrogen source and from a haploid state. The meiotic defect caused by the mutations in mat and mei3 genes is bypassed by pat], whereas the mei2 mutation suppresses the pat] mutation. On the basis of these facts, Iino and Yamamoto (12) proposed a negative control mechanism for meiosis in the fission yeast. The model suggests that pat] products repress mei2 activity to block the initiation of meiosis under nitrogen-rich growth conditions. Thus, derepression of mei2 activity appears to be a key step for the induction of meiosis.To elucidate the regulatory network operating during the initiation of meiosis, we cloned the mei2 gene and studied its transcriptional regulation. MATERIALS AND METHODSStrains and culture conditions. The S. pombe and Escherichia coli strains used in the present study are listed in Table 1. E. coli cells were cultured in L broth at 37°C. When

Connatal tuberculosis should be considered in neonatal respiratory infection resistant to antibiotics. Prevention of transmission of tuberculosis on the neonatal intensive care unit by chemoprophylaxis is important.

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