Figure 29.4:Alternate splicing occurs in 2 steps and form 2 different protein

Processing of rRNA: Eukaryotes have 80s ribosomes and prokaryotes have 70s ribosomes. Ribosomal RNAs are transcribed as long precursor sequence which is then modified at specific bases and cleaved to give mature products. In both bacteria and eukaryotes rRNA processing involves two basic steps of cleavage and base modification.

rRNA processing in Bacteria: rRNA precursor in bacteria is a 30s rRNA which modified and cleaved to give 23s rRNA, 16s rRNA, 5s rRNA and some t-RNA segments in between are also there sometimes. 30s pre- rRNA transcript consist of 16s rRNA sequence followed by spacer which may have t-RNA sequence in some cases and then there is 23s rRNA sequence followed by 5s rRNA sequence near to 3’ end. At times there is one more t-RNA sequence after 5s rRNA sequence at 3’ end. There are seven different genes for rRNA in E.coli, they are essentially similar in sequence of rRNA segments but differ with number and sequence of t-RNA segments.