Translation factors Translation factors are proteins used at only one step of the translation process They are not permanent components of the ribosome, but cycle on and off
Translation factors • Translation factors are proteins used at only one step of the translation process • They are not permanent components of the ribosome, but cycle on and off
Translation factors Approximate Number Factor per Ribosome in Cell Binds GTP? Role Initiation IF1 1/7 Promotes dissociation of 70s rIBosome IF2 17 Ye Helps attach initiator tRNA IF3 1/7 No Similar to lfl Elongation EF-Tu 10 Yes Carries trna into a site EF-TS Yes Participates in recharging Ef-tu with gTp EF-G Ye Facilitates translocation Termination RFl 1/20 Release factor(UAA, UAG) RF2 l/20 N Release factor (UAA, UGA) RF3 Yes A GTPase that promotes release
Translation factors
Initiation ·翻译的起始是在mRNA上装配核糖体复合物的过程。 翻译总是从起始密码子AUG开始的,由一个特定的起 始tRNA所识别,加入第一个氨基酸为Met。在原核生 物中这个Met被修饰为N-甲酰Met 甲酰化是在Me连接到tRNA后,由转甲酰基酶转移 N1o- formyltetrahydrofolate(四氢叶酸)的甲酰基而成的 ·在 E coli中还有转运合成过程中Me的tRNA,这两种 tRNA都是由甲硫氦酰-tRNA合成酶催化而成的,但这 两种甲硫氨酰tRNA是不同的 initial fMet-tRNA. tMet ● internal Met- RNA Met
Initiation • 翻译的起始是在mRNA上装配核糖体复合物的过程。 翻译总是从起始密码子AUG开始的，由一个特定的起 始tRNA 所识别，加入第一个氨基酸为Met。在原核生 物中这个Met被修饰为N-甲酰Met • 甲酰化是在Met连接到tRNA后，由转甲酰基酶转移 N10-formyltetrahydrofolate (四氢叶酸)的甲酰基而成的 • 在E.coli中还有转运合成过程中Met的tRNA，这两种 tRNA都是由甲硫氨酰-tRNA合成酶催化而成的，但这 两种甲硫氨酰tRNA是不同的 • initial fMet-tRNAi fMet • internal Met-tRNAm Met
起始tRNA和延长tRNA的差别 (1)Met-RNAM在受体臂 末端的一对碱基是GC,在 Fo(甲酰甲 fMet-tRNAM是CA,C可 硫氨酸) 以和延伸因子IF-2结合 C A ACCA ·(2) tRNa Me在反密码子环的 茎上有3对G-C,若发生突变 将会阻止其进入P位点。 (3 tRNAf的反密码子环上 的是A, tRNA. M是烷基化 腺嘌呤。 A tRNa et Tyc环端是A, CAU CAU tRNAfMet的相应位置是G 作用不清。 The difference between initiate tRNAFMet and elongate tRNAm-Met
起始tRNA和延长tRNA的差别 • ⑴ Met-tRNAm Met在受体臂 末端的一对碱基是GC，在 fMet-tRNAf Met是CA，C可 以和延伸因子IF-2结合。 • ⑵tRNAf Met在反密码子环的 茎上有3对G-C,若发生突变 将会阻止其进入P位点。 • ⑶tRNAf Met的反密码子环上 的是A，tRNAm Met是烷基化 腺嘌呤。 • tRNAf Met TψC环端是 A， tRNAmMet的相应位置是G， 作用不清
Factors and components needed for initiation Small ribosomal subunit ·mRNA IF3- initiation factor 3: keep ribosomal subunits apart IFl= initiation factor 1: assist binding of IF2? IF2= initiation factor 2 In complex with gTP, it brings fmet-tRNAf to the partial P site on the small subunit Activates a gtPase activity in the small subunit, which allows dissociation of f2. f3 and f1 fmet-tRNAf GTP Binding of large subunit to the initiation complex gives a complete ribosome ready for elongation
Factors and components needed for initiation • Small ribosomal subunit • mRNA • IF3 = initiation factor 3: keep ribosomal subunits apart • IF1= initiation factor 1: assist binding of IF2? • IF2 = initiation factor 2 – In complex with GTP, it brings fmet-tRNAf to the partial P site on the small subunit. – Activates a GTPase activity in the small subunit, which allows dissociation of IF2, IF3, and IF1. • fmet-tRNAf • GTP • Binding of large subunit to the initiation complex gives a complete ribosome ready for elongation