In Streptomyces griseus, A‐factor (2‐isocapryloyl‐3R‐hydroxymethyl‐γ‐butyrolactone) at an extremely low concentration triggers streptomycin biosynthesis and cell differentiation by binding a repressor‐type receptor protein (ArpA) and dissociating it from DNA. An A‐factor‐responsive transcriptional activator (AdpA) able to bind the promoter of strR, a pathway‐specific regulatory gene responsible for transcription of other streptomycin biosynthetic genes, was purified to homogeneity and adpA was cloned by PCR on the basis of amino acid sequences of purified AdpA. adpA encoding a 405‐amino‐acid protein containing a helix‐turn‐helix DNA‐binding motif at the central region showed sequence similarity to transcriptional regulators in the AraC/XylS family. The −35 and −10 regions of the adpA promoter were found to be a target of ArpA; ArpA bound the promoter region in the absence of A‐factor and exogenous addition of A‐factor to the DNA–ArpA complex immediately released ArpA from the DNA. Consistent with this, S1 nuclease mapping showed that adpA was transcribed only in the presence of A‐factor and strR was transcribed only in the presence of intact adpA. Furthermore, adpA disruptants produced no streptomycin and overexpression of adpA caused the wild‐type S. griseus strain to produce streptomycin at an earlier growth stage in a larger amount. On the basis of these findings, we propose here a model to demonstrate how A‐factor triggers streptomycin biosynthesis at a late exponential growth stage.
In Streptomyces griseus, A-factor (2-isocapryloyl-3R-hydroxymethyl-␥-butyrolactone) serves as a microbial hormone that switches on many genes required for streptomycin production and morphological development. An open reading frame (Orf1) showing high sequence similarity to oligoribonucleases of various origins is present just downstream of adpA, one of the A-factor-dependent genes. Orf1 was named OrnA (oligoribonuclease A) because it showed 3-to-5 exo-oligoribonuclease activity, releasing [ 32 P]CMP from ApCpC[ 32 P]pC used as a substrate. Reverse transcription-PCR and S1 nuclease mapping analyses revealed that ornA was transcribed from two promoters; one was a developmentally regulated, A-factor-dependent promoter in front of adpA, and the other was a constitutive promoter in front of the ornA coding sequence. Transcription of ornA was thus additively enhanced at the initiation stage for secondary metabolism and aerial mycelium formation. ornA-disrupted strains grew slowly and scarcely formed aerial mycelium. ornA homologues were distributed in a wide variety of Streptomyces species, including S. coelicolor A3(2), as determined by Southern hybridization analysis. Disruption of the ornA homologue in S. coelicolor A3(2) also caused phenotypes similar to those of the S. griseus ⌬ornA strains. The OrnA oligoribonucleases in Streptomyces species are therefore not essential but play an important role in vegetative growth and in the initiation of differentiation.The filamentous, soil-inhabiting, gram-positive bacterial genus Streptomyces is characterized by the ability to produce a wide variety of secondary metabolites and by complex morphological differentiation culminating in sporulation (5). In Streptomyces griseus, A-factor (2-isocapryloyl-3R-hydroxymethyl-␥-butyrolactone) is required for streptomycin (Sm) production and cell differentiation (13-15). A-factor at an extremely low concentration triggers Sm production and aerial mycelium formation by binding a repressor-type receptor protein (ArpA) and dissociating it from the DNA (23, 24). Recently we identified adpA, which encodes a transcriptional activator for strR, a pathway-specific regulatory gene responsible for transcription of other Sm biosynthetic genes, as one of the target genes of ArpA (22). ArpA binds the adpA promoter and represses its transcription in the absence of A-factor during early growth phase. adpA is thus developmentally regulated by A-factor. During these studies, we found an open reading frame (Orf1) showing end-to-end similarity to the oligoribonuclease of Escherichia coli (31) only 10 bp downstream from the termination codon of adpA. Because orf1 is located just downstream of adpA and was expected to be developmentally regulated by A-factor and because little is known about RNA degradation in members of Streptomyces with a complex life cycle, we analyzed the enzyme activity of Orf1 and disrupted orf1 to examine the function of the gene product.Exo-oligoribonuclease activity of Orf1. Orf1 shows high sequence similarity (44% identity) to ...
Recently, enhanced development to full term was obtained with embryos reconstructed with bovine early G1 cells rather than with G0 cells (Kasinathan et al. 2001 Nat. Biotechnol. 19, 1176-1178; Urakawa et al. 2004 Theriogenology 62, 714-728). However, the reason why donor somatic cells at the early G1 phase are better for embryo reconstruction is unclear. In this study, we investigated the relation of spatial gene expression patterns at the 4- to 8-cell stage to blastocyst development of embryos reconstructed with early G1 cells. Bovine fibroblasts stably transfected with �-act/luc+/IRES/EGFP were used for embryo reconstruction. M phase cells were prepared as described by Urakawa et al. (2004). Early G1 cells were obtained from cultured M phase cells soon after the M phase cells divided. Quiescent cells (cultured in 0.4% serum for 7 days) were used as G0 cells for a control. The cells were electrofused with enucleated bovine oocytes matured in vitro, and activated with a calcium ionophore and cycloheximide. The reconstructed embryos were cultured until 60 hours post fusion (hpf), and zonae pellucidae of 4- to 8-cell embryos were removed by pronase. To determine gene expression, the LUC+ activity (luminescence) in the embryo blastomeres was detected with an imaging photon counter (Hamamatsu Photonics, Hamamatsu City, Shikuoka Prefecture, Japan) for 10 min. The embryos were categorized as being positive, mosaic, or negative depending on whether all, some or no blastomeres were luminescent, respectively. The embryos were cultured in mSOF medium individually until 168 hpf to assess development to the blastocyst stage. Blastocyst development of reconstructed embryos without detection of luminescence was also examined. Experiments were repeated three times, and the data were analyzed with Fisher's PLSD test following ANOVA. At 60 hpf, 75% (74/99) of embryos reconstructed with early G1 cells and 55% (46/83) of embryos with G0 cells developed to 4- to 8-cell stage embryos. The difference is significant (P < 0.05). The percentages of positive, mosaic, and negative embryos with G1 cells were 49, 35 and 16%, and blastocyst rates were 30, 11, and 0%, respectively. With G0 cells, the percentages were 32, 56, and 12%, and the blastocyst rates were 15, 4, and 0%, respectively. More positive embryos were obtained with early G1 cells than with G0 cells (P < 0.05). Blastocyst rates of the positive embryos with early G1 cells were the same as with G0 cells (P > 0.05). Blastocyst development of positive embryos was higher than that of mosaic and negative embryos in early G1 and G0 groups (P < 0.05). Without detection of luminescence, the blastocyst rates from the reconstructed embryos were 43% (35/81) and 16% (20/125) with early G1 and G0 cells, respectively (P < 0.05). These results suggest that the higher developmental capacity of embryos reconstructed with early G1 cells might be related to the appropriate spatial gene expression at the 4- to 8-cell stage. A part of this study was supported by a grant from the Wakayama Prefecture Collaboration of Regional Entities for the Advancement of Technological Excellence of the JST.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.