Columbia Pictures announced yesterday that it has restructured its New York publicity department, bringing in former PMK Public Relations Agency praiser Mara Buxbaum and former Nancy Seltzer & Associates praiser Elizabeth Clark as senior publicists.Buxbaum and Clark are de facto replacements for Lynn Fischoff and Corin Nelson, who ankled their Columbia Pictures publicity posts in December. Working under the wing of PMK agency partner Lois Smith, Buxbaum was account executive on director Louis Malle’s “Damage” and Robert Redford’s “A River Runs Through It.” Her individual representation included such clients as Cher, Mary Tyler Moore and Timothy Hutton. As a senior account executive for Nancy Seltzer & Associates, Clark’s movie accounts included Columbia’s “A Few Good Men and “Misery,” as well as Orion Pictures’ “The Silence of the Lambs” and Paramount Pictures upcoming release “Indecent Proposal.” Completing the restructuring, Sabrina Laufer has been promoted to the position of junior publicist for Columbia’s East Coast office. Laufer was an assistant publicist for Columbia over the last three years. The moves follow the departure of senior veepee publicity and promotion Sue Barton and the addition of veepee of East Coast Publicity Stephen Klain, who was brought on late in 1992 . Barton has since formed a consulting firm in Pacific Grove, Calif.