Characterization of the Human DNA Methyltransferase Splice Variant Dnmt1b
Bibliographic record
Abstract
Tissue- and gene-specific patterns of cytosine-DNA methylation are characteristic features of vertebrate genomes. The generation and proper maintenance of DNA methylation patterns are essential for embryonic development, as demonstrated by the lethal phenotypes of mice with either a targeted disruption of Dnmt1, the gene responsible for the maintenance of DNA methylation, or targeted disruption of Dnmt3a or Dnmt3b, the genes involved in generation of newly formed methylation patterns. Recently, a novel mRNA, Dnmt1b, resulting from alternative splicing of Dnmt1 was identified (Hsu, D. W., Lin, M. J., Lee, T. L., Wen, S. C., Chen, X., and Shen, C. K., (1999) Proc. Natl. Acad. Sci. U. S. A. 96, 9751-9756). The abundance of Dnmt1b mRNA was estimated by semiquantitative reverse transcription polymerase chain reaction and was suggested to encode a major C-5 DNA methyltransferase isoform. Here we report characterization of this novel DNA methyltransferase transcript, Dnmt1b, and its protein product in human cell lines and in freshly isolated human peripheral blood mononuclear cells. The abundance of Dnmt1b transcript, as determined by quantitative RNase protection analysis, was determined to range from 6% to 25% of Dnmt1 in human cells. Second generation antisense inhibitors targeted to the 5'- and 3'-ends of Dnmt1 inhibited the accumulation of both Dnmt1 and Dnmt1b in cells. Dnmt1b protein purified from a baculovirus expression system was demonstrated to be a functional DNA methyltransferase, and to have Michaelis constants for both DNA and S-adenosyl-L-methionine similar to baculovirus-expressed Dnmt1. However, antibodies raised against Dnmt1b epitopes demonstrated that Dnmt1b protein was present at approximately 2-5% of the level of Dnmt1 and therefore represents only a minor DNA methyltransferase isoform in human cells.
Fetched live from OpenAlex and de-inverted. Abstracts are not stored in this database: the inverted indexes are 8.6 GB of the frame’s 9.3 GB of text, and the host has 13 GB free.
How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.001 | 0.001 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".