Granules defined by timing of biosynthesis of their characteristic proteins. The granules formed at any given stage of maturation of neutrophil precursors will be composed of the granule proteins synthesized at that time. The different subsets of granules identified are the result of differences in the biosynthetic windows of the various granule proteins during maturation and not the result of specific sorting between individual granule subsets. When the formation of granules ceases, secretory vesicles will form337 (this point has not yet been proven). The control of biosynthesis is exerted by transcription factors that control the expression of genes for the various granule proteins. It cannot be ruled out that posttranscriptional control occurs so that biosynthesis of proteins is not a precise reflection of the corresponding mRNA levels. MB, myeloblast; PMC, promyelocyte; MC, myelocyte; MMC, metamyelocyte; BC, band cell; Segm., segmented cell.