Question

RNA polymerase-I transcribes eukaryotic ribosomes which do not consist of
(a) 28S rRNA
(b) 5S rRNA
(c) 5.8S rRNA
(d) 18S rRNA

Answer 1

This is the only rRNA synthesised by the RNA polymerase- III otherwise in the higher eukaryotic all the rRNA is transcribed by RNA polymerase- I.

Complete answer step by step:
- RNA polymerase-I is located in the nucleolus and synthesizes 28s, 18s and 5.8 s RNA
- RNA polymerase-I is an enzyme that copies DNA to rRNA and which account for over 50% of RNA synthesis.
- The rate of transcription is lower than RNA polymerase- II which is only 20 nucleotides.
- In bacteria 5s RNA and another larger RNA along with the number of associated proteins is known as 23s RNA.
- RNA polymerase-II is located in the nucleoplasm and synthesizes hnRNA or mRNA and some snRNA.
- RNA polymerase-II is located in the nucleoplasm and synthesizes tRNA, some snRNA and 5s rRNA.
- In E. coli it is observed that deletion of the 5S rRNA gene reduces the protein synthesis rate.
- In eukaryotes, 5S rRNA interacts only with L5 ribosomal protein whereas in prokaryotes 5S rRNA binds with L5, L18, and L25 ribosomal protein.
- 5S rRNA is identified as a specialized covariance model which incorporates information on the pronounced sequence composition and structure variation.
So, the correct answer is, ‘5S rRNA.’

Note:
- All types of RNA in the cell can be inhibited by rifampicin and actinomycin D binds to the DNA preventing transcription.
- In yeast, the 5s RNA has the different features of lying inside the rDNA repeat and it is flanked by a non- transcribed spacer which is transcribed backwards by pol- III separated from the rest of rDNA.