Question

Explain with examples the concept of jumping genes in prokaryotes

Answer 1

• Jumping genes are those those sequences in DNA which can move from one site in the genome to another site in the genome.
• They are also called transposons. Transposons may directly move from one site to another via DNA intermediate or RNA intermediate.
• Mostly in prokaryotes , jumping genes transpose via DNA intermediate. This means an additional copy of that gene is made and transposed to a new location (the original gene remains at the original site ).
• Examples of transposons in bacteria include IS (insertion sequence) elements , Tn elements like Tn9 (chloramphenicol resistance) , etc.
• Transposition of a jumping gene increases its number of copies in the genome. Upon translocation, some sequences may get lost at the site where jumping gene is being transposed.
• General structure of jumping gene : let us consider IS elements. Structurally IS elements are flanked by specific sequences at both ends. These are inverted repeats of ~50 nucleotides, which flank both ends of IS elements oriented in opposite directions. The central region (IS element) consists of protein coding sequence and encodes for enzymes required for transposition - (enzyme: transposase).

• Other elements like Tn9 elements may contain more than one protein coding region between the two flanking ends of inverted repeats.