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K Stuart

Publications and source records attributed to K Stuart.

At least 91 records · Page 5Linked to original sources
PubMed1991

Cycles of progressive realignment of gRNA with mRNA in RNA editing.

We characterized numerous partially edited NADH dehydrogenase 7 and ATPase 6 cDNAs. Most of these have a stretch of incompletely edited sequence at the junction of mature and unedited sequences. The characteristics of the junctions suggest editing of sites multiple times and that editing within each junction does not proceed precisely 3' to 5'. Analyses of gRNAs and corresponding junction sequences predict a series of progressively more stable, but incompletely base-paired, interactions in the junction region. The predicted interactions suggest that the gRNA is progressively realigned with the mRNA being edited. We suggest that gRNA interactions with the mRNA result in regions of lower thermodynamic stability that are selected for editing, thus driving toward the most stable structure, the complete gRNA/mRNA duplex.

Adenosine Triphosphatases↗
PubMed1991

The two ATPase 6 mRNAs of Leishmania tarentolae differ at their 3' ends.

We have determined the complete nucleotide sequence of ATPase 6 mRNA from Leishmania tarentolae. RNA editing occurs only in the 5' one-third of the mRNA and is the most extensive observed to date in this species. We have identified a potential gRNA sequence, encoded in a minicircle, for a portion of the edited sequence. The predicted amino acid sequence is about 85% homologous to that predicted from the more extensively edited Trypanosoma brucei ATPase 6 mRNA. The edited L. tarentolae mRNA exists as two distinct size classes which differ in the size of their 3' ends. Although variation in the length of the 3' untranslated region cannot be excluded, the size difference is probably to be due to variation in the length of the poly(A) tail.

Adenosine Triphosphatases↗
PubMed1991

A DNA sequence (LD1) which occurs in several genomic organizations in Leishmania.

Leishmania DNA 1 (LD1) is a 27.5-kb sequence that occurs in all 91 stocks of twelve New and Old World Leishmania species examined; related sequences are present in some other kinetoplastid species. LD1 has no homology to several DNA sequences that are amplified in drug-resistant Leishmania. LD1 occurs in 3 different genomic organizations in Leishmania, depending on the stock. It is present within large (1.5-2 megabase) chromosomes in all stocks, and 74 stocks contain only this form. In 12 other stocks, LD1 also occurs in smaller (less than 550 kb) chromosomes, some of which are multicopy. Five stocks contain LD1 in multicopy circular DNA molecules in addition to the sequences found in the larger chromosome(s). Restriction fragment length polymorphisms of LD1 sequences correlate with taxonomic grouping, suggsting that LD1 is an endogenous sequence.

Animals↗
PubMed1991

RNA editing in mitochondrial mRNA of trypanosomatids.

The editing of mRNA coding sequences by the modification, removal or addition of nucleotides has recently been recognized as another form of RNA processing. Studies of the extensive editing of mitochondrial mRNAs in trypanosomatids have revealed the involvement of small guide RNAs (gRNAs) which are encoded by the minicircles of kinetoplast DNA.

Animals↗
PubMed1991

RNA editing in kinetoplastid protozoa.

RNA editing produces mature mRNAs by adding and removing uridines within the mitochondrial transcripts. The edited sequence appears to be specified by small complementary RNAs using a non-templated process that may have features resembling RNA splicing. The accumulation of edited mRNAs is developmentally regulated.

Animals↗
PubMed1990

The MURF3 gene of T. brucei contains multiple domains of extensive editing and is homologous to a subunit of NADH dehydrogenase.

Mitochondrial MURF3 transcripts of T. brucei are extensively edited by the addition and deletion of uridines. The editing creates potential initiation and termination codons and a continuous open reading frame. The predicted amino acid sequence has homology to a subunit of NADH dehydrogenase (ND7). ND7 is independently edited in two distinct domains, suggesting two editing initiation sites. Editing in the two domains is differentially regulated: the 5' domain is edited in both bloodstream and procyclic forms but the 3' domain is completely edited only in the bloodstream form. Two potential guide RNA (gRNA) coding sequences were identified in the same minicircle. One is complementary to edited sequence in the 5' domain, the other to edited sequence in the 3' domain.

Amino Acid Sequence↗
PubMed1990

An extensively edited mitochondrial transcript in kinetoplastids encodes a protein homologous to ATPase subunit 6.

The mitochondrial MURF4 gene of T. brucei has pronounced G versus C strand bias and heterogeneously sized transcripts, characteristic of genes encoding extensively edited transcripts. We find that MURF4 transcripts of T. brucei are extensively edited throughout by the addition and deletion of numerous uridines, creating potential initiation and termination codons and a continuous open reading frame. A potential guide RNA sequence occurs in a minicircle between inverted repeats. The 5' region of L. tarentolae MURF4 transcripts is also extensively edited, with a created initiation codon. The predicted MURF4 amino acid sequences have homology to those of mitochondrial ATP-ase subunit 6 genes from a variety of organisms. In addition, their hydropathic profiles are quite similar to those of other species. We therefore conclude that MURF4 encodes ATPase subunit 6 genes.

Adenosine Triphosphatases↗
PubMed1990

A retroposon in the 5' flank of a Trypanosoma brucei VSG gene lacks insertional terminal repeats.

A retroposon-like repeated sequence, ingi, occurs in high copy number in the genome of Trypanosoma brucei brucei. An ingi is present in the 5' flank of the 5C gene, an intrachromosomal IsTat 1.5 variant surface glycoprotein (VSG) gene family member. The 5' end of the ingi is located 22 bp upstream of the putative VSG start codon and the ingi open reading frame is in the opposite orientation to that of the VSG gene. The termini of the ingi are not flanked by a short repeat sequence and there are no sequences upstream of the ingi insertion which are homologous to the 5' flanking sequence of other 5 VSG gene family members. Thus, it appears that recombination and/or gene conversion between two ingi sequences may have eliminated the original 5C gene flanking sequence. Similar events may also have occurred with all but one previously reported ingi.

Amino Acid Sequence↗
PubMed1990

The trypanosome leucine repeat gene in the variant surface glycoprotein expression site encodes a putative metal-binding domain and a region resembling protein-binding domains of yeast, Drosophila, and mammalian proteins.

We have identified a new variant surface glycoprotein expression site-associated gene (ESAG) in Trypanosoma brucei, the trypanosome leucine repeat (T-LR) gene. Like most other ESAGs, it is expressed in a life cycle stage-specific manner. The N-terminal 20% of the predicted T-LR protein resembles the metal-binding domains of nucleic acid-binding proteins. The remainder is composed of leucine-rich repeats that are characteristic of protein-binding domains found in a variety of other eucaryote proteins. This is the first report of leucine-rich repeats and potential nucleic acid-binding domains on the same protein. The T-LR gene is adjacent to ESAG 4, which has homology to the catalytic domain of adenylate cyclase. This is intriguing, since yeast adenylate cyclase has a leucine-rich repeat regulatory domain. The leucine-rich repeat and putative metal-binding domains suggest a possible regulatory role that may involve adenylate cyclase activity or nucleic acid binding.

Animals↗
PubMed1989

RNA editing: the creation of nucleotide sequences in mRNA--a minireview.

RNA editing changes the nucleotide sequence of mRNAs that are encoded in genes which contain the sequences in an abbreviated form. Editing adds uridines that are not encoded in the gene to the transcripts and less frequently removes encoded uridines. The process appears to be posttranscriptional and to proceed in the 3'-to-5' direction. Some sites may undergo multiple editings until the final sequence is produced; in some cases uridines may be added and subsequently removed. A general hypothesis is proposed that predicts a series of reactions that may occur in association with a macromolecular complex, the editosome, which interacts with a multinucleotide region.

Animals↗
PubMed1989

Transcripts from the co-transposed segment of variant surface glycoprotein genes are in Trypanosoma brucei polyribosomes.

In Trypanosoma brucei the 5' proximal flanking sequences of a variant surface glycoprotein (VSG) gene, the co-transposed segment, are transcribed in a variant antigenic type- and stage-specific fashion along with the VSG gene. The precursor transcripts are subsequently processed to yield smaller transcripts from the co-transposed segment as well as the VSG mRNA. These co-transposed segment transcripts are quite abundant, polyadenylated and contain the spliced leader sequence, all characteristics of trypanosome mRNAs. We have found that all of the co-transposed segment transcripts from two VSG genes are present in polyribosomes. The nucleotide sequence of much of the co-transposed segment of one of these VSG genes, however, has no open reading frames coding for proteins longer than 49 amino acids. These results suggest that co-transposed segment transcripts do not encode essential proteins even though they are present in polyribosomes and may be translated.

Animals↗
PubMed1989

Trypanosoma brucei: conserved sequence organization 3' to telomeric variant surface glycoprotein genes.

We have previously postulated that telomeric variant surface glycoprotein (VSG) genes in Trypanosoma brucei serve more frequently than intrachromosomal VSG genes as basic copies for gene conversion. To examine this further we determined the sequence for approximately 1200 nucleotides 3' to the telomeric IsTat 1 VSG gene, expressed in early variant antigenic types, and compared this sequence with those 3' to other VSG genes. We found that about 200 nucleotides immediately 3' to the 1 VSG gene are homologous to sequences immediately 3' to other telomeric VSG genes. These sequences may function in extended duplex formation 3' to telomeric VSG genes and partially explain their more frequent gene conversion. In addition, further 3' is a highly conserved 49 bp direct repeat, which is not transcribed into stable RNA. These sequences appear to be conserved in various T. brucei stocks, and we have therefore proposed a model which is a modification of one previously proposed (E. H. Blackburn and P. B. Challoner, 1984, Cell, 36, 447-457; L. H. T. Van der Ploeg, A. Y. C. Liu, and P. Borst, 1984, Cell, 36, 459-468) for the sequence organization of a trypanosome telomeric region.

Amino Acid Sequence↗
PubMed1989

Trypanosomatids: mitochondrial RNA editing.

RNA editing is a genetic regulatory process that was recently discovered in the mitochondrion of trypanosomatid parasites. It alters mRNA by the addition and deletion of uridines. Much remains to be learned about this process, including identification and characterization of the macromolecules that catalyze and regulate this process and the mechanism of editing.

Animals↗