Nucleus is the centre of the regulation of cell activities since it contains the hereditary material, DNA,carrying the information forprotein synthesis. The DNA is bound up with histone protein to form chromatin. The nucleus contains one or more nucleoli in which ribosome subnits,ribosomal RNA,and transfer RNA are manufactured. The nucleus is surrounded by a double nuclear membrane,crossed by a number of nuclear pores. The nucleus is continuous with the endoplasmic reticulum. There is usually only one nucleus per cell,although there may be many in very large cells such as those of striated (skeletal) muscle. Such multinucleate cells are calld coenocytes.