The subunit composition of the holoenzyme of the enzyme RNA polymerase in bacteria is:
• 2 subunits
• 1 subunit
• 1 subunit
The functional roles of the various subunits given above are:
The two subunits have a role of binding to DNA and also are instrumental for the proper assembling of the holoenzyme.
The two subunits are also needed along with the two subunits for binding to DNA. These subunits have an additional function of the catalytic synthesis of RNA.
The subunit is important for the assembly of the core enzyme.
The subunit is the most important subunit of all. It is instrumental in the recognition of the - 10 and the - 35 promoter sequences in DNA.
The holoenzyme is required for the initiation of transcription.
The factor is instrumental in the recognition of the - 10 and the - 35 promoter sequences in DNA.
The recognition and binding of the factor to DNA on the molecular level can be explained in this way:
After attachment of the holoenzyme of RNA polymerase, the whole enzyme slides along the DNA strand. The factor can slide along the major groove of the DNA where the - 10 and the - 35 promoter sequences are present.
While sliding, the factor is able to recognize the bases in the major groove of DNA. In this way, it recognizes the promoter sequences in the major groove. When the factor meets a promoter sequence, hydrogen bonding occurs.
Hydrogen bonding occurs between the factor and the nucleotide bases of the promoter sequences. This interaction is specific and thus the binding is very tight.
The different DNA sequences are given below:
The term consensus sequence indicates that the sequences have some conserved bases and some variable bases. The sequences are seen in almost all organisms without much variation.
The consensus sequence for the above DNA sequence is GGCATTGTCA. This consensus sequence can be determined by finding out the most common nucleotides for each position of the sequence.
There are slight variations in each organism but the sequence usually remains the same.