The membrane surface of polarized epithelial cells can be divided in a
pical and basolateral domains that differ in molecular composition and
function. Components of the cytoskeleton are involved in critical ste
ps of both generation and maintenance of cell polarity. Generation of
polarity is controlled by microtubules that serve as uniformly aligned
and polarized cytoplasmic guiding structures for the vectorial and se
lective transport of Golgi-derived carrier vesicles to the apical cell
surface. Targeting of membrane proteins to the basolateral cell surfa
ce does not depend on microtubules but follows the constitutive bulk f
low of membranes. Once inserted into the lipid bilayer several membran
e proteins such as the kidney anion exchanger 1 (AE1) and the sodium p
ump become immobilized at specialized microdomains of the lateral cell
surface. Evidence is provided that both membrane proteins are linked
via ankyrin to the spectrin-based membrane cytoskeleton that underlies
the basolateral membrane domain. Linkage of these and other integral
membrane proteins to the cytoskeleton may not only place them to speci
alized sites of the plasma membrane but may also prevent these transpo
rters from clustering and endocytosis, thus helping them to stay at th
e cell surface. In search of sequence motifs involved in binding of in
tegral membrane proteins to components of the cytoskeleton we found th
at the binding interface of AE1 to protein 4.1 (an actin and spectrin
cross-linking protein) consists of a cluster of five amino acid residu
es, namely IRRRY in AE1 and LEEDY on protein 4.1. This motif may play
a more general role in cytoskeleton membrane linkages.