We describe the first virus-like particle of a hyperthermophilic euryarchaeote which was discovered in a strain of "Pyrococcus abyssi" previously characterized in our laboratory. This particle, named PAV1, is lemonshaped (120 nm ؋ 80 nm), with a short tail terminated by fibers, and resembles the virus SSV1, the type member of the Fuselloviridae, isolated from Sulfolobus shibatae. Sensitivity of the virus-like particle to organic solvents and detergents suggested that the envelope of PAV1 may contain lipids in addition to proteins. It contains a double-stranded circular DNA of 18 kb which is also present in high copy number in a free form in the host cytoplasm. No integrated form of the PAV1 genome could be detected in the host chromosome. Under standard growth conditions, the host cells continuously release PAV1 particles into the culture supernatant without spontaneous lysis, with a maximum reached in the late stationary phase. UV, gamma irradiation, treatment with mitomycin C, and various physiological stresses had no effect on PAV1 production. Screening of a large number of Thermococcales isolates did not permit to find a sensitive host. These results suggest that PAV1 persists in the host strain in a stable carrier state rather than a prophage.The Archaea domain comprises two major phyla, namely, the Crenarchaeota, including the extremely thermophilic sulfur-metabolizing Archaea of the orders Sulfolobales and Thermoproteales, and the Euryarchaeota, containing mainly the methanogens, the extreme halophiles, and the hyperthermophilic order Thermococcales (29). Our knowledge about archaeal viruses is still rather limited, and among known archaeal viruses that have been reported, only few have been studied in detail at the molecular level.All known crenarchaeotal viruses display unusual morphotypes and compose three novel families which were created to account for their unique features, namely, the filamentous Lipothrixviridae (2, 13, 32), the lemon-shaped Fuselloviridae (18,25), and the rod-shaped Rudiviridae (20). The dropletshaped Guttaviridae (3) have not yet been established as an acknowledged virus family. The best studied virus is the lemonshaped SSV1, whose original host is the hyperthermophile Sulfolobus shibatae. SSV1 is temperate and forms stable lysogens by site specifically inserting its 15.5-kb circular genome into the host chromosome (31). Its complete nucleotide sequence has been determined (19). In contrast, all but two of the as-yet-described viruses of extreme halophiles and methanogens have the classical head-and-tail morphology typical of many bacterial phages and have therefore been assigned to the virus families Myoviridae or Siphoviridae (1). There are two known exceptions, both showing a lemon-shaped morphology resembling SSV1, the type member of the Fuselloviridae. The first one was described as a virus-like particle (VLP) isolated from M. voltae strain A3 containing a circular double-stranded DNA of 23 kb, of which an integrated copy was found in the host chromosome (30). The second ex...
The pl gene encodes a regulatory protein that controls the transcription of a number of structural genes of the anthocyanin biosynthetic pathway i n maize. pl alleles have been classified phenotypically into two categories: dominant (Pr) alleles lead to intense, light-independent pigmentation in vegetative and floral organs of the plant; recessive "sun-red" alleles (pr) lead to light-dependent red pigmentation in which only tissues exposed to light become pigmented. Based on these observations, two alternate pathways leading to anthocyanin synthesis in the plant have been proposed: one requiring light and the other bypassing the light requirement through the action of Pl. To evaluate this hypothesis, we have analyzed light-independent and light-dependent alleles of pl. Sequence analysis revealed that the two types of alleles have very distinct promoters but have the capacity to encode very similar proteins. The protein encoded by one recessive allele was shown to be functional in transient assays. Measurements of husk mRNA levels by quantitative polymerase chain reaction showed that sun-red pl alleles are expressed at much lower levels than a Pl allele, but their expression is increased approximately sixfold by exposure to light. These results lead to the conclusion that the sun-red pl alleles are not null; instead, they synthesize functional mRNA and protein. We propose that the light-dependent pigmentation observed in pl plants is the result of a threshold effect in which light exposure boosts pl mRNA expression past a crucial level necessary to generate sufficient PL protein molecules to activate transcription of the anthocyanin structural genes.
Pioneer Hi-Bred International, Johnston, lowa 50130-0038The pl gene encodes a regulatory protein that controls the transcription of a number of structural genes of the anthocyanin biosynthetic pathway i n maize. pl alleles have been classified phenotypically into two categories: dominant (Pr) alleles lead to intense, light-independent pigmentation in vegetative and floral organs of the plant; recessive "sun-red" alleles (pr) lead to light-dependent red pigmentation in which only tissues exposed to light become pigmented. Based on these observations, two alternate pathways leading to anthocyanin synthesis in the plant have been proposed: one requiring light and the other bypassing the light requirement through the action of Pl. To evaluate this hypothesis, we have analyzed light-independent and light-dependent alleles of pl. Sequence analysis revealed that the two types of alleles have very distinct promoters but have the capacity to encode very similar proteins. The protein encoded by one recessive allele was shown to be functional in transient assays. Measurements of husk mRNA levels by quantitative polymerase chain reaction showed that sun-red pl alleles are expressed at much lower levels than a Pl allele, but their expression is increased approximately sixfold by exposure to light. These results lead to the conclusion that the sun-red pl alleles are not null; instead, they synthesize functional mRNA and protein. We propose that the light-dependent pigmentation observed in pl plants is the result of a threshold effect in which light exposure boosts pl mRNA expression past a crucial level necessary to generate sufficient PL protein molecules to activate transcription of the anthocyanin structural genes.
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.