(mental note: set up Errata sub-forum today)
Yes. A bow mounted turretted gun can fire at an enemy target in either of the port, bow or starboard arcs. A stern-mounted turretted gun can fire at an enemy target in either of the port, stern or starboard arcs.
Note: not all bow or stern guns need be turretted. Bow and stern casemate/barbette arrangements existed, and exist.
There are currently no rules released for side-mounted turrets (in reality, wing turrets often had little ability to fire forward), ventral turrets or disappearing guns

W.