Radial organization of nuclei with peripheral gene-poor chromosomes and central gene-rich chromosomes is common and could depend on the nuclear boundary as a scaffold or position marker. To test this, we studied the role of the ubiquitous nuclear envelope (NE) component lamin B1 in NE stability, chromosome territory position, and gene expression. The stability of the lamin B1 lamina is dependent on lamin endoproteolysis (by Rce1) but not carboxymethylation (by Icmt), whereas lamin C lamina stability is not affected by the loss of full-length lamin B1 or its processing. Comparison of wild-type murine fibroblasts with fibroblasts lacking full-length lamin B1, or defective in CAAX processing, identified genes that depend on a stable processed lamin B1 lamina for normal expression. We also demonstrate that the position of mouse chromosome 18 but not 19 is dependent on such a stable nuclear lamina. The results implicate processed lamin B1 in the control of gene expression as well as chromosome position.