The un-17 mutant was originally isolated as an irreparable temperature-sensitive (ts) mutant in Neurospora crassa. Early experiments showed that cells of this mutant immediately stopped growing and died when the temperature of the culture was shifted from a permissive temperature (25°C) to non-permissive temperature (35°C). This ts phenotype is suppressed by addition of cycloheximide or in some conditions of growth repression. Even at the permissive temperature, it shows a female sterile phenotype and is deficient in production of exocellular superoxide dismutase SOD4 (EC 18.104.22.168). By searching for a DNA fragment that complements the ts phenotype of the un-17 mutant from a N. crassa genome library, we found the un-17 gene. The cloned un-17 gene encodes a homolog of the Saccharomyces cerevisiae poly(A) polymerase (PAP). The un-17 mutant had a one-base substitution mutation in the gene. The cloned un-17 genes from the wild-type strain and the un-17 mutant were introduced into both the un-17 mutant and wild-type strain. The un-17 mutant introduced by un-17 DNA from the wild-type strain showed recovery of both the ts and female sterile phenotypes. Moreover, the purified product derived from the wild-type strain showed PAP activity in vitro. These findings indicate that the un-17 mutant carries a ts mutation in the gene encoding PAP.
Hordatines A and B, the strong antifungal compounds in barley (Hordeum vulgare), are biosynthesized from p-coumaroyl- and feruloyl-CoA and agmatine by two successive reactions catalyzed by agmatine coumaroyltransferase (ACT) and peroxidase. ACT catalyzes the formation of agmatine conjugates (p-coumaroylagmatine and feruloylagmatine) from precursor CoAs and agmatine, and peroxidase catalyzes the oxidative coupling of agmatine conjugates to form hordatines. Our previous study demonstrated that the short arm of barley chromosome 2H (2HS) is responsible for the biosynthesis of hordatines. In the present study, however, barley genes encoding the ACT (HvACT) and a peroxidase (HvPrx7) were found to be located on the long arm of 2H (2HL). The amounts of hordatines and precursor agmatine conjugates were analyzed in wheat (Triticum aestivum) and wheat lines carrying a whole 2H chromosome, 2HS or 2HL. The addition of 2H and 2HL elevated the levels of agmatine conjugates in wheat. This could be attributed to the HvACT on 2HL. However, the content of agmatine conjugates increased also in the 2HS addition line, suggesting the presence of another unidentified ACT gene on 2HS. Hordatines were detected in wheat, but their content was by far lower than those in barley. The 2H and 2HS addition lines accumulated substantial amounts of hordatines, while the 2HL addition line accumulated them as little as wheat did in spite of the substantial transcription of the HvPrx7 gene on 2HL and of the increased accumulation of the precursor agmatine conjugates. These facts suggest that the HvPrx7 gene on 2HL is not involved in the hordatine biosynthesis and that unidentified peroxidase gene responsible for the hordatine biosynthesis is located on 2HS in barley.
Generally, oaks dominate the broadleaf deciduous forests in Japan. The genetic variation in 6 cpDNA regions (trnT-trnL, trnL-trnF, atpB-rbcL, and trnH-psbA speacers, trnL intron, and matK gene) with regard to the Japanese oak (Quercus mongolica var. crispula) and 3 related species in the section Prinus (Q.serrata, Q.dentata and Q. aliena) was investigated in 598 trees belonging to 44 populations distributed throughout the Japanese archipelago. Additional samples were collected from Korea, China, and Russia (Sakhalin). Thirteen haplotypes (I to XIII) were identified on the bases of 15 nucleotide substitutions and 3 indels. Haplotypes I and II were discovered in northeastern Japan, whereas haplotypes III to IX were distributed in southwestern Japan. The boundary distinguishing these 2 groups was located in central Japan coincident with the Itoigawa-Shzuoka tectonic line. Haplotype I was also found in Sakhalin, whereas haplotypes VI, VII, VIII, X, XI, XII, and XIII were found in Korea and China. Four oak species in the same location shared identical haplotypes, suggesting cpDNA introgression by occasional hybridization. Both the values of total haplotype diversity (HT) and haplotype diversity within populations (HS) in Q. mongolica var. crispula were higher in the southwestern populations than in the northeastern populations. A haplotype network indicated that haplotype VI is the ancestral haplotype. The presence of identical haplotypes in Korea, China, and Japan suggested that the haplotypes diversified on the Eurasian continent before the last glacial period. The difference in genetic structure between the northeastern and southwestern regions indicates a difference in the history of migration and recolonization in Japan during the last glacial period.
A latitudinal cline in characteristics associated with the P DNA transposable element is well known in eastern Australian populations of Drosophila melanogaster. In order to survey the long-term patterns of P-M system characteristics and genomic P element content, we established 292 isofemale lines from 54 localities in 1996–1997 and evaluated them for gonadal dysgenesis (GD) sterility and the ratio of KP to full-size P elements (KP/FP ratio). The results were compared to those from collections made in 1983–1986 and 1991–1994. Over 10–14 years, 1) the cross A GD scores of the northern-middle populations declined dramatically; 2) the clinal pattern of the cross A* GD scores did not change; 3) the latitudinal pattern of the KP/FP ratio did not change. The results suggest that only a few P elements determine P-M characteristics and that there has been selection for genomes with fewer active P elements, but not for a great change in proportions of size classes.
Schizosaccharomyces pombe has two paralogues of 3-methyladenine DNA glycosylase, Mag1p and Mag2p, which share homology with Escherichia coli AlkA. To clarify the function of these redundant enzymes in base excision repair (BER) of alkylation damage, we performed several genetic analyses. The mag1 and mag2 single mutants as well as the double mutant showed no obvious methyl methanesulfonate (MMS) sensitivity. Deletion of mag1 or mag2 from an nth1 mutant resulted in tolerance to MMS damage, indicating that both enzymes generate AP sites in vivo by removal of methylated bases. A rad16 mutant that is deficient in nucleotide excision repair (NER) exhibited moderate MMS sensitivity. Deletion of mag1 from the rad16 mutant greatly enhanced MMS sensitivity, and the mag2 deletion also weakened the resistance to MMS of the rad16 mutant. A mag1/mag2/rad16 triple mutant was most sensitive to MMS. These results suggest that the NER pathway obscures the mag1 and mag2 functions in MMS resistance and that both paralogues initiate the BER pathway of MMS-induced DNA damage at the same level in NER-deficient cells or that Mag2p tends to make a little lower contribution than Mag1p. Mag1p and Mag2p functioned additively in vivo. Expression of mag1 and mag2 in the triple mutant confirmed the contribution of Mag1p and Mag2p to BER of MMS resistance.