COPII proteins are necessary to generate secretory vesicles at the endoplasmic reticulum. In yeast, the Sec24p protein is the only COPII component in which two close orthologues have been identified. By using gene knock-out in yeast, we found that the absence of one of these Sec24 orthologues resulted in a selective secretion defect for a subset of proteins released into the medium. Data base searches revealed the existence of an entire family of Sec24-related proteins in humans, worms, flies, and plants. We identified and cloned two new human cDNAs encoding proteins homologous to yeast Sec24p, in addition to two human cDNAs already present within the data bases. The entire Sec24 family identified to date is characterized by clusters of highly conserved residues within the 2/3 carboxyl-terminal domain of all the proteins and a divergent amino terminus domain. Human (h) Sec24 orthologues co-immunoprecipitate with hSec23Ap and migrate as a complex by size exclusion chromatography. Immunofluorescence microscopy confirmed that these proteins co-localize with hSec23p and hSec13p. Together, our data suggest that in addition to its role in the shaping up of the vesicle, the Sec23-24p complex may be implicated in cargo selection and concentration.
Eukaryotic DNA polymerase  and the reverse transcriptases are the most inaccurate of the known DNA polymerases. We report here mutagenic replication in vitro past intrastrand N(7)G-N(7)G chelates of the cisdiamminedichloroplatinum(II), the major DNA adduct of the antitumor agent cisplatin by calf thymus DNA polymerase  and human immunodeficiency virus type I reverse transcriptase (42% and 26% mutations, respectively). The most frequent modifications generated by both enzymes were one-base frameshift deletions. Only one mutational hot spot opposite the platinated guanines was observed with human immunodeficiency virus type I reverse transcriptase, while two hot spots were generated by DNA polymerase , one at the base situated 5 to the lesion and the other situated 4 -6 nucleotides 5 to the adduct. An unusual mutagenic event, tandem replication of a 12-base pair sequence, was observed with DNA polymerase . The mutational spectra of the two DNA polymerases suggest that template slippage occurred with higher frequency in the presence of the more distributive DNA polymerase .The molecular mechanisms of mutagenesis are not well understood. One general pathway is thought to involve errorprone replication past unrepaired DNA damage. Bulky DNA lesions can result from cellular exposure to agents such as UV light or a variety of chemical carcinogens. Studies performed in vivo indicate that mammalian cells possess the ability to circumvent blocks to DNA synthesis and are able to replicate in the presence of these lesions (1-4). In vitro, it has been demonstrated that a number of purified cellular DNA polymerases can replicate through bulky adducts. For example, calf thymus DNA polymerase ␦ has been shown to replicate past cis-synand trans-syn-cyclobutane-thymine dimers in the presence of proliferating cell nuclear antigen (5). We have recently shown that an intrastrand cross-link formed by the anticancer and mutagenic agent cis-diamminedichloroplatinum(II) (cisplatin) blocked calf thymus DNA polymerases ␣, ␦, and ⑀, while DNA polymerase  is capable of replicating past the lesion (6). This Pt-d(GpG) 1 adduct was placed at the N-7 position of the two adjacent guanine bases of codon 13 of the human HRAS gene. DNA polymerase , the structurally simplest of the five known mammalian DNA polymerases, is believed to function primarily in the repair of damaged DNA. It is a monomeric protein of 335 amino acids (39 kDa) that lacks exonuclease activities and works in a distributive manner, although it is capable of processive gap-filling synthesis on single-stranded DNA templates for up to 6 nucleotides (7). DNA polymerase  appears to be the least accurate of the eukaryotic DNA polymerases in replicating undamaged DNA in vitro (8, 9). Human immunodeficiency virus reverse transcriptase (HIV-1 RT) also catalyzes highly error-prone replication (10 -14) and shows structural homology with DNA polymerase  (15).The mutagenic consequences of the replicative bypass of a single Pt-d(GpG) adduct in vitro are unknown. We compare here the...
DANA is the first SINE isolated from zebrafish (Danio rerio) exhibiting all the hallmarks of these tRNA-derived elements. DANA is unique in its clearly defined substructure of distinct cassettes. In contrast to generic SINE elements, DANA appears to have been assembled by insertions of short sequences into a progenitor, tRNA-derived element. Once associated with each other, these subunits were amplified as a new transposable element with such a remarkable success that DANA-related sequences comprise 10% of the modern zebrafish genome. At least some of the sequences comprised by the full-length element were capable of movement, forming a new group of mobile, composite transposons, one of which caused an insertional mutation in the zebrafish no tail gene. Being present only in the genus Danio, and estimated to be as old as the genus itself, DANA may have played a role in Danio speciation by massive amplification and genome-wide dispersion. There are extensive DNA polymorphisms betweeit zebrafish populations and strains detected by PCR amplification using primers specific to DANA, suggesting that the DANA element will be useful as a molecular tool for genetic and phylogenetic analyses.SINEs (short interspersed elements) are typically nonviral retrotransposable DNA sequences that use RNA as an intermediate of transposition and are prevalent components of eukaryotic genomes (reviewed in refs.
OVO controls germline and epidermis differentiation in flies and mice. In the Drosophila germline, alternative OVO-B and OVO-A isoforms have a common DNA-binding domain, but different N-termini. We show that these isoforms are transcription factors with opposite regulatory activities. Using yeast one-hybrid assays, we identified a strong activation domain within a common region and a counteracting repression domain within the OVO-A-specific region. In flies, OVO-B positively regulated the ovarian tumor promoter, while OVO-A was a negative regulator of the ovarian tumor and ovo promoters. OVO-B isoforms supplied ovo(+) function in the female germline and epidermis, while OVO-A isoforms had dominant-negative activity in both tissues. Moreover, elevated expression of OVO-A resulted in maternal-effect lethality while the absence of OVO-A resulted in maternal-effect sterility. Our data indicate that tight regulation of antagonistic OVO-B and OVO-A isoforms is critical for germline formation and differentiation.
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.