© 1991 Nature Publishing Group http://www.nature.com/naturebiotechnology
© 1991 Nature Publishing Group http://www.nature.com/naturebiotechnology
© 1991 Nature Publishing Group http://www.nature.com/naturebiotechnology
© 1991 Nature Publishing Group http://www.nature.com/naturebiotechnology
© 1991 Nature Publishing Group http://www.nature.com/naturebiotechnology
© 1991 Nature Publishing Group http://www.nature.com/naturebiotechnology