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posted by fyngyrz on Wednesday April 25 2018, @12:32AM   Printer-friendly
from the Drugs-N-Alcohol-no-wait-that's-the-wrong dept.

A new DNA structure inside human cells known as the “i-motif”, has been identified by scientists.  

This form resembles a twisted “knot” of DNA, instead of the well-known double helix first described by James Watson and Francis Crick.

Lab work has previously suggested the existence of DNA in this form, but this is the first time it has been observed in living cells.

The scientists are not exactly sure what the function the i-motif is, but they suspect it is involved with the process of “reading” DNA sequences and converting them into useful substances.

[...]

A conventional strand of DNA is made up of “base pairings”. The building blocks of the double helix are substances called bases – adenine, thymine, cytosine and guanine.

In a world first, Garvan researchers have identified a new four-stranded 'tangled knot' structure that comes and goes in the DNA of living human cells.

In a world first, Australian researchers have identified a new DNA structure – called the i-motif – inside cells. A twisted 'knot' of DNA, the i-motif has never before been directly seen inside living cells.

[...] "When most of us think of DNA, we think of the double helix," says Associate Professor Daniel Christ, Head of the Antibody Therapeutics Lab at Garvan and and a conjoint Associate Professor in UNSW Medicine, who co-led the research. "This new research reminds us that totally different DNA structures exist and could well be important for our cells."

"The i-motif is a four-stranded 'knot' of DNA," says Associate Professor Marcel Dinger, Head,of the Kinghorn Centre for Clinical Genomics at Garvan, who co-led the research with Associate Professor Christ. "In the knot structure, C letters on the same strand of DNA bind to each other – so this is very different from a double helix, where 'letters' on opposite strands recognise each other, and where Cs bind to Gs [guanines]."

Although researchers have seen the i-motif before and have studied it in detail, it has only been witnessed in vitro – that is, under artificial conditions in the laboratory, and not inside cells. In fact, scientists in the field have debated whether i-motif 'knots' would exist at all inside living things – a question that is resolved by the new findings.

I-motif DNA structures are formed in the nuclei of human cells (DOI: 10.1038/s41557-018-0046-3) (DX)

Human genome function is underpinned by the primary storage of genetic information in canonical B-form DNA, with a second layer of DNA structure providing regulatory control. I-motif structures are thought to form in cytosine-rich regions of the genome and to have regulatory functions; however, in vivo evidence for the existence of such structures has so far remained elusive. Here we report the generation and characterization of an antibody fragment (iMab) that recognizes i-motif structures with high selectivity and affinity, enabling the detection of i-motifs in the nuclei of human cells. We demonstrate that the in vivo formation of such structures is cell-cycle and pH dependent. Furthermore, we provide evidence that i-motif structures are formed in regulatory regions of the human genome, including promoters and telomeric regions. Our results support the notion that i-motif structures provide key regulatory roles in the genome.


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