First thought came to mind was Japanese origin. The style of finish of the stays at the rear dropouts, and the short fluted seat stay caps. Those shifter bosses were popular around the aero craze era. Both Shimano and Suntour had offered 'aero' shifters. Even Campy if I recall. Thank goodness it didn't last long.
Looks to be a quality frame. The head tube lugs should be helpful to ID it.
"N"...Nishiki?