Cln3

G1/S-specific cyclin Cln3 is a protein that is encoded by the CLN3 gene. The Cln3 protein is a budding yeast G1 cyclin that controls the timing of Start, the point of commitment to a mitotic cell cycle. It is an upstream regulator of the other G1 cyclins, and it is thought to be the key regulator linking cell growth to cell cycle progression. It is a 65 kD, unstable protein; like other cyclins, it functions by binding and activating cyclin-dependent kinase (CDK).

Cln3 in Start regulation

Cln3 regulates Start, the point at which budding yeast commit to the G1/S transition and thus a round of mitotic division. It was first identified as a gene controlling this process in the 1980s; research over the past few decades has provided a mechanistic understanding of its function.

Identification of CLN3 gene

The CLN3 gene was originally identified as the whi1-1 allele in a screen for small size mutants of Saccharomyces cerevisiae (for Cln3's role in size control, see below). This screen was inspired by a similar study in Schizosaccharomyces pombe, in which the Wee1 gene was identified as an inhibitor of cell cycle progression that maintained normal cell size. Thus, the WHI1 gene was at first thought to perform a size control function analogous to that of Wee1 in pombe. However, it was later found that WHI1 was in fact a positive regulator of Start, as its deletion caused cells to delay in G1 and grow larger than wild-type cells. The original WHI1-1 allele (changed from whi1-1 because it is a dominant allele) in fact contained a nonsense mutation that removed a degradation-promoting PEST sequence from the Whi1 protein and thus accelerated G1 progression.WHI1 was furthermore found to be a cyclin homologue, and it was shown that simultaneous deletion of WHI1—renamed CLN3—and the previously identified G1 cyclins, CLN1 and CLN2, caused permanent G1 arrest. This showed that the three G1 cyclins were responsible for controlling Start entry in budding yeast.

Cln3 (disambiguation)

Cln3 may refer to:

Chlorine azide

Chlorine azide (ClN₃) is an inorganic compound that was discovered in 1908 by Friedrich Raschig. Concentrated ClN
3 is notoriously unstable and may spontaneously detonate at any temperature.

Preparation and handling

Chlorine azide is prepared by passing chlorine gas over silver azide, or by an addition of acetic acid to a solution of sodium hypochlorite and sodium azide.

When treated with ammonia it is conceivable that one or more of the three possible azinamines, NH₂N₃, NH(N₃)₂, and N(N₃)₃ may be formed.

Explosive characteristics

Chlorine azide is extremely sensitive. It may explode, sometimes even without apparent provocation; it is thus too sensitive to be used commercially unless first diluted in solution. Chlorine azide reacts explosively with 1,3-butadiene, ethane, ethene, methane, propane, phosphorus, silver azide, and sodium. On contact with acid, chlorine azide decomposes, evolving toxic and corrosive hydrogen chloride gas.

Regulatory information

Its shipment is strictly regulated by the US Department of Transportation.