Abstract: The object of the present invention is to provide a gene of a protein having an enzyme activity which makes it possible to regulate or control the content of saturated fatty acids and unsaturated fatty acids in plant cells, and an enzyme protein as the expression product. There is disclosed a protein with a KASII enzyme activity which has a specific amino acid sequence, typically the amino acid sequence of a &bgr;-ketoacyl-ACP synthetase II (KASII) enzyme protein derived from cyanobacterium (Anacystis nidulans) or substantially the same amino acid sequence as the one described above. There is also disclosed a KASII enzyme protein gene coding for the amino acid sequence of the above described protein. Furthermore, there are disclosed a recombinant vector which comprises said gene, and a cell into which said gene has been introduced.