YAOUNDE (Reuters) - The central bank of the six-nation Central African CEMAC zone has cut its prime lending rate by 25 basis points to 3.25 percent to help spur the economy as it revised down its 2013 growth forecast to 2.6 percent from 4.1 percent. The bank's governor, Lucas Abaga Nchama, said in a statement late on Friday that the slow down in economic activity was due to a decline in public investments and oil production. The CEMAC zone is made up of Cameroon, Central African Republic, Chad, Congo-Brazzaville, Equatorial Guinea and Gabon. Five of them produce oil, which accounts for 36 percent of the region's GDP and 87 percent of total exports.