The revolving door is turning again at R.J. Reynolds Tobacco Co. with James W. Johnston, chairman-CEO of R.J. Reynolds Tobacco Worldwide departing. Mr. Johnston, 50, last July lost control of the U.S. subsidiary but regained it late '95. The company said Mr. Johnston was leaving the tobacco company as well as his vice chairman post at parent RJR Nabisco Holding Corp. to spend time with his family. The departure, effective June 30, comes after RJR Chairman Mike Harper left May 2. No successor to Mr. Johnston has been named.