Progression of the cell cycle through mitosis leads to abortion of nascent transcripts

Abstract

SummaryNascent transcripts of the Drosophila Ubx gene were detected by in situ hybridization. Following onset of expression, the progress of RNA polymerase (1.4 kb/min) across the gene was visualized as the successive appearance of hybridization signals from different positions within the transcription unit. Nascent transcripts disappeared at mitosis. Hybridization signals reappeared in the next cell cycle first with a 5′ probe, and later, following a delay consistent with the transcription rate, with a 3′ probe. Nascent transcripts were observed continuously in expressing cells of a mutant embryo in which cells are blocked in interphase. We conclude that progression through mitosis causes abortion of nascent transcripts and suggest that periodic abortion of transcription contributes to regulation of expression of large genes.

Partially Assembled Nucleosome Structures at Atomic Detail

“…While atomistic modeling is arguably (62,63) the only method available at the moment that can deliver the transient PANS at full atomic resolution, the method (64) cannot yet probe timescales of seconds relevant to key biological processes such as transcription (65), which depend critically on the DNA packing in the nucleosome. Here, the difficulty is overcome by verifying experimentally that the key geometric characteristics of the modeled structures, including the length of protected DNA, remain close to the observed values on the AFM timescales of minutes.…”

“…In fact, characteristic timescales for spontaneous DNA unwrapping deep inside the nucleosome can reach 10 min, and possibly even longer for sites further away from the entry/exit (10). This very slow unwrapping kinetics undoubtedly reduces the speed of Pol II machinery considerably-unimpeded, the latter can transcribe the entire nucleosomal DNA in seconds (65).…”

The PROSPERO transcription factor is asymmetrically localized to the cell cortex during neuroblast mitosis in Drosophila

“…We think the same pros protein is moving from the GMC cortex into the nucleus, because the process occurs too rapidly for de novo synthesis of new pros in the GMC. The pros gene is >23 kb (data not shown), and would take over 20 minutes to transcribe and translate (Thummel et al, 1990;Shermoen and O'Farrell, 1991); we observe nuclear localization rapidly after mitosis (see Results). However, it is possible that pros RNA is inherited by the GMC and could be rapidly translated and localized to the nucleus.…”

Big genes and little genes and deadlines for transcription

“…Nascent Ultrabithorax transcripts are aborted as cells pass through mitosis 3 , reappearance of completed transcripts in the next cell cycle being delayed by the 55 minutes required for the task. In cells that initiate transcription of Ultrabithorax too late in the cell cycle, the arrival of mitosis prevents completion of transcripts.…”

“…The mammalian RNA polymerase working at its rate of about 3 kilobases (kb) per minute (37 °C) requires roughly 11 hours to traverse the gargantuan (2,000-kb) dystrophin gene. Measurements 2,3 of the lag between initiation at a promoter and transcription of downstream sequences have shown that the Drosophila polymerase progresses at about 1.4 kb per minute (25 °C). At this rate, 55 minutes are required for transcription of the Ultrabithorax gene, whereas only 2 are needed for the shorter knirps gene.…”