Directing the McCarter Theatre\'s production of \"Gem of the Ocean\" was a perfect fit for actor Ruben Santiago-Hudson and for more than one reason, he explains, while sipping coffee at Princeton \'s Carousel restaurant the other day. Not only had he acted the key role of Caesar in the Broadway production of the acclaimed August Wilson play, but Santiago-Hudson had a strong personal reaction to the play\'s unique female main character. That remarkable Wilson creation, Aunt Ester, a 285-year-old keeper of wisdom and understanding (played in this production as on Broadway by Phylicia Rashad), reminded Santiago-Hudson of Nanny, the wise and loving caretaker who brought him up in Lackawanna, N.Y., in the 1950s. And it was Nanny who Santiago-Hudson immortalized, first in his Obie-winning one-man play \"Lackawanna Blues,\" then in the expanded version he wrote and sold to HBO. After graduating from SUNY Binghamton, where he says a professor encouraged him to apply for further study, Santiago-Hudson won a scholarship to study for a master\'s degree at Wayne State University .