发布: 2017年06月20日第7卷第12期 DOI: 10.21769/BioProtoc.2336 浏览次数: 8690
评审: Gal HaimovichMelike ÇağlayanAnonymous reviewer(s)
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Abstract
It recently has been established that adenine-containing cofactors, including nicotinamide adenine dinucleotide (NAD+), reduced nicotinamide adenine dinucleotide (NADH), and 3’-desphospho-coenzyme A (dpCoA), can serve as ‘non-canonical initiating nucleotides’ (NCINs) for transcription initiation by bacterial and eukaryotic cellular RNA polymerases (RNAPs) and that the efficiency of the reaction is determined by promoter sequence (Bird et al., 2016). Here we describe a protocol to quantify the relative efficiencies of transcription initiation using an NCIN vs. transcription initiation using a nucleoside triphosphate (NTP) for a given promoter sequence.
Keywords: RNA polymerase (RNA聚合酶)Background
Transcription in bacteria, archaea, and eukaryotes is carried out by multi-subunit RNA polymerases (RNAPs) conserved in sequence, structure, and mechanism (Ebright, 2000; Lane and Darst, 2010). To initiate transcription, RNAP, together with one or more initiation factors, binds to a specific DNA sequence referred to as a ‘promoter’ and unwinds promoter DNA to form an RNAP-promoter open complex (RPo) containing an unwound ‘transcription bubble’ (Figure 1A; Ruff et al., 2015). RNAP then selects a transcription start site by expanding (‘scrunching’) or contracting (‘antiscrunching’) the transcription bubble to place transcription-start-site nucleotides in the RNAP active-center initiating site (‘i site’) and extending site (‘i+1 site’), binds a complementary initiating nucleotide substrate in the i site and a complementary extending substrate in the ‘i+1’ site, and catalyzes phosphodiester-bond formation to yield an initial RNA product (Winkelman et al., 2016).
In standard de novo transcription initiation, the initiating substrate is a nucleoside triphosphate (NTP), typically ATP or GTP (Nickels and Dove, 2011). However, recently it has been established that adenine-containing cofactors, including nicotinamide adenine dinucleotide (NAD+), reduced nicotinamide adenine dinucleotide (NADH), and 3’-desphospho-coenzyme A (dpCoA), can serve as alternative initiating substrates (‘non-canonical initiating nucleotides’; NCINs), yielding NCIN-capped RNA products that have distinctive 5’-end structures, stabilities, and translation efficiencies (Figures 1B-1C; Bird et al., 2016; Barvik et al., 2016; Jiao et al., 2017; Walters et al., 2017). It further has been established that the relative efficiencies of NCIN-mediated initiation vs. NTP-mediated initiation are determined by promoter sequence (Bird et al., 2016).
Here, we describe a protocol to determine the relative efficiencies of NCIN-mediated transcription initiation versus ATP-mediated transcription initiation, (kcat/KM, NCIN)/(kcat/KM, ATP), for a given promoter sequence. The protocol involves generating radiolabeled initial RNA products in a set of transcription reactions having a constant concentration of NCIN and varying concentrations of ATP, followed by quantifying NCIN-initiated RNA and total RNA, followed by plotting observed ratios of NCIN-initiated RNA to total RNA as a function of ratios of NCIN concentration to ATP concentration.
Figure 1. Transcription initiation. A. RNAP-promoter open complex (RPo) with unwound transcription bubble. Gray, RNAP; blue, -10-element nucleotides; i and i+1, RNAP active-center initiating nucleotide binding site and extending nucleotide binding site; boxes, DNA nucleotides (nontemplate-strand nucleotides above template-strand nucleotides). B. Structures of ATP and NAD+, Red, identical atoms in ATP and NAD+; C. Initial RNA products formed in transcription initiation using ATP (top) or transcription initiation using NAD+ (bottom). Left subpanels show initiating ATP or NAD+ bound in i site; right subpanels show initial RNA products formed using CTP as extending nucleotide. Red boxes, adenosine and cytosine moieties of ATP, NAD+, and CTP; green boxes, nicotinamide-riboside moiety of NAD+.
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文章信息
版权信息
© 2017 The Authors; exclusive licensee Bio-protocol LLC.
如何引用
Bird, J. G., Nickels, B. E. and Ebright, R. H. (2017). RNA Capping by Transcription Initiation with Non-canonical Initiating Nucleotides (NCINs): Determination of Relative Efficiencies of Transcription Initiation with NCINs and NTPs. Bio-protocol 7(12): e2336. DOI: 10.21769/BioProtoc.2336.
分类
微生物学 > 微生物生物化学 > RNA
分子生物学 > RNA > 转录
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