The distribution of microtubule-associated protein lB (MAPlB) phosphorylated by either
proline-directed protein kinase (PDPK) or casein kinase II (CK II) in neuroblastoma cells and
hippocampal neurons has been studied by immunofluorescence using specific antibodies to
distinct phosphorylation-sensitive epitopes. A proximo-distal gradient of increasing PDPK-
catalyzed phosphorylation of MAPlB is superimposed on a proximo distal gradient of
decreasing CK II-catalyzed MAPlB phosphorylation within growing axon-like neurites …