  The shapes of cell membranes are largely regulated by membrane associated,
curvature active, proteins. We use a numerical model of the membrane with
elongated membrane inclusions, recently developed by us, which posses
spontaneous directional curvatures that could be different along and
perpendicular to its long axis. We show that, due to membrane mediated
interactions these curvature inducing membrane nematogens can oligomerize
spontaneously, even at low concentrations, and change the local shape of the
membrane. We demonstrate that for a large group of such inclusions, where the
two spontaneous curvatures have equal sign, the tubular conformation and
sometime the sheet conformation of the membrane are the common equilibrium
shapes. We elucidate the factors necessary for the formation of these {\it
protein lattices}. Furthermore, the elastic properties of the tubes, like their
compressional stiffness and persistence length are calculated. Finally, we
discuss the possible role of nematic disclination in capping and branching of
the tubular membranes.
