8 public questions tagged with this topic.
Guanosyl transferase adds a methylated cap to the 5' end of eukaryotic mRNA to enhance stability and translation.
Ref: NCERT Class 12 Biology Chapter 5: Molecular Basis of Inheritance Human Genome Project and DNA Fingerprinting
The poly-A tail protects eukaryotic mRNA from degradation and aids in translation efficiency.
Ref: NCERT Class 12 Biology Chapter 5: Molecular Basis of Inheritance Post-Transcriptional Modifications - Capping Splicing Polyadenylation
The poly-A tail protects eukaryotic mRNA from degradation and aids in translation.
Ref: NCERT Class 12 Biology Chapter 5: Molecular Basis of Inheritance DNA Replication - Semiconservative and Machinery
Mature mammalian messenger RNAs carry polyadenine tail of approximately eighty to two hundred nucleotides on average, longer two hundred to two hundred fifty in newly synthesized nuclear RNAs shortened in cytoplasm, while yeast tails average seventy to eighty residues. Initial addition of ten to twelve adenines is slow distributive phase, then nuclear polyadenine binding protein PABPN1 stimulates processive synthesis to full length. Tail length influences binding of one PABPC per twenty-seven adenines, forming compact ribonucleoprotein particle. Progressive deadenylation by CCR4-NOT complex in cytoplasm regulates translation and decay. Oocyte cytoplasmic polyadenylation lengthens tails to activate translation.
Ref: Alberts et al., Molecular Biology of the Cell, 7th ed., Chapter 6: Poly(A) tail length 80-200; Lodish 9th ed., Regulation of poly(A) length
After cleavage at polyadenylation site, polyadenine tail is synthesized not by RNA polymerase II but by specialized nuclear polyadenine polymerase PAPOLA and PAPOLG, recruited through interaction with CPSF via FIP1 subunit and stimulated by nuclear polyadenine binding protein PABPN1. Enzyme is template independent, uses ATP to add adenylates processively: initial distributive addition of ten to twelve adenines, then PABPN1-dependent switch to processive synthesis of two hundred to two hundred fifty residues in mammals. Polyadenine tail enhances stability, export, and translation via PABPC and eIF4G circularization bridge.
Ref: Alberts et al., Molecular Biology of the Cell, 7th ed., Chapter 6: Poly(A) polymerase adds tail; Lodish 9th ed., Mechanism of polyadenylation
Eukaryotic pre-mRNAs contain conserved hexamer AAUAAA twenty to thirty nucleotides upstream of cleavage site, transcribed into RNA as polyadenylation signal essential for three prime end formation. Cleavage and polyadenylation specificity factor CPSF binds AAUAAA via WDR33 and CPSF30 zinc fingers recognizing sequence via base stacking interactions, while cleavage stimulation factor CstF binds downstream GU-rich downstream sequence element. Polyadenylation factors CFI, CFII, and endonuclease CPSF73 catalyze endonucleolytic cut. Signal AAUAAA is essential: single point mutation drastically reduces processing. Similar DNA sequence AATAAA in coding strand is classic Hogness box.
Ref: Lodish et al., Molecular Cell Biology, 9th ed., Chapter 10: Polyadenylation signal AAUAAA recognition by CPSF; Alberts 7th ed., 3' end formation signals
Eukaryotic five prime cap harbors highly unusual five prime to five prime linkage instead of canonical three prime to five prime phosphodiester found in RNA backbone. After RNA triphosphatase generates diphosphate RNA, guanylyltransferase hydrolyzes GTP to GMP and catalyzes attack of diphosphate RNA on alpha phosphate forming Gp pppN triphosphate bridge linking guanine five prime to first nucleotide five prime. Three phosphate groups create 5'-5' connection. Subsequent methylation at N7 of guanine and ribose 2' O positions generate cap zero, cap one, cap two structures resistant to decapping and exonuclease attack.
Ref: Berg et al., Biochemistry, 9th ed., Chapter 28: 5'-5' triphosphate cap linkage; Lodish 9th ed., Mechanism of guanylyltransferase forms unusual linkage
monocistronic is the scientifically accurate answer to this question. Within the study of Acid, Base, pH, this concept is well-established through extensive research and is documented in standard scientific literature. The specific properties, mechanisms, or characteristics of monocistronic directly address what is being asked. Among the other options, polycistronic, overlapping, and non-coding do not correctly answer this question because they either refer to different concepts, describe properties of other molecules or processes, or represent common misconceptions about this topic.
Ref: Lehninger Principles of Biochemistry, Nelson & Cox, 8th Ed., Ch. 2
