Interchromatin granules (that is a cluster of granules) of varying size, but mostly rounded areas, are found in the nuclei of mammalian cells. These are clustered in the nucleus, especially in and around apoptosis as seen in the lower magnification electron micrograph on the left below. They are, according to concensus, composed partly of pre-mRNA splicing factors.  They are not static structures, and are active sites of transcription, size can be several microns or hundreds of microns in diameter.  They were found in a study done years ago, to be really prominent in late phases of apoptosis. The image on the right shows particularly well (though the micrograph is not sterling by any means) that they are composed of 20–25 nm granules that are connected like beads on a chain by thin fibrils (also visible).  The red dots in each of these two images (the right image enlarged from red box on the left) are the size of ribosomes, and the bar markers then are 10 times bigger (270 nm).  There are at least 3 other interchromatin granule clusters in the micrograph on the left. That shows the beads in the right hand enlargement to be just around 20-25 nm in diameter (something a little smaller than the accepted middle size of a ribosome (27 nm) (selected from the same micrograph.

Interchromatin granules may be collections of snRNPs and other RNA processing components involved in producing mRNA. These granules are so evenly spaced as to be a marvel.  neg 14138_block 61002 HeLa cells, UV and inhibitor of caspase 1. (BTW, dont ask what the dense areas to the right of the interchromatin granule cluster is…. ha ha)