NAD regulates nucleotide metabolism and genomic DNA replication.

The intricate orchestration of enzymatic activities involving nicotinamide adenine dinucleotide (NAD) is essential for maintaining metabolic homeostasis and preserving genomic integrity. As a co-enzyme, NAD plays a key role in regulating metabolic pathways, such as glycolysis and Kreb's cycle. ADP-ribosyltransferases (PARPs) and sirtuins rely on NAD to mediate post-translational modifications of target proteins.

MDC1 maintains active elongation complexes of RNA polymerase II.

The role of MDC1 in the DNA damage response has been extensively studied; however, its impact on other cellular processes is not well understood. Here, we describe the role of MDC1 in transcription as a regulator of RNA polymerase II (RNAPII). Depletion of MDC1 causes a genome-wide reduction in the abundance of actively engaged RNAPII elongation complexes throughout the gene body of protein-encoding genes under unperturbed conditions.

Large Intronic Deletion of the Fragile Site Gene Dramatically Lowers Its Fragility Without Impacting Gene Expression.

Common chromosomal fragile sites (CFSs) are genomic regions prone to form breaks and gaps on metaphase chromosomes during conditions of replication stress. Moreover, CFSs are hotspots for deletions and amplifications in cancer genomes. Fragility at CFSs is caused by transcription of extremely large genes, which contributes to replication problems.

Common Chromosomal Fragile Sites-Conserved Failure Stories.

In order to pass on an intact copy of the genome during cell division, complete and faithful DNA replication is crucial. Yet, certain areas of the genome are intrinsically challenging to replicate, which manifests as high local mutation propensity. Such regions include trinucleotide repeat sequences, common chromosomal fragile sites (CFSs), and early replicating fragile sites (ERFSs).