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Of no legal validity, force, or effect; nothing. As used in the phrase null and void, refers to something that binds no one or is incapable of giving rise to any rights or duties under any circumstances.

West's Encyclopedia of American Law, edition 2. Copyright 2008 The Gale Group, Inc. All rights reserved.

NULL. Properly, that which does not exist; that which is not in the nature of things. In a figurative sense it signifies that which has no more effect than if it did not exist. 8 Toull. n. 320.

A Law Dictionary, Adapted to the Constitution and Laws of the United States. By John Bouvier. Published 1856.
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Abbreviations: ACTH, adrenocorticotroph adenoma; GH, growth hormone adenoma; GH+, Pit-1 family member with strong growth hormone and a lesser degree of prolactin or thyroid-stimulating hormone (TSH) staining; Gon, gonadotroph adenoma; Null, null cell adenoma; Pit1, Pit-1 family member (not otherwise specified); PlurGH, plurihormonal growth hormone adenoma; PlurGH+, plurihormonal growth hormone adenoma with lesser degrees of prolactin or TSH staining; PRL, prolactinoma; PRL+, Pit-1 family member with strong prolactin staining and lesser degree of growth hormone or thyrotropin staining; TSH+, TSH-producing adenoma with lesser degree of GH staining; Unk, unknown.
Lane M: [lambda] DNA digested with Pst I used as marker; Lane 1: Total RNA extracted from null cells used as control RNA for reverse transcription and PCR amplification, no band corresponding to epo gene seen; Lanes 2, 3, 4 and 5: template RNA 0.5 [micro]g, 1.0 [micro]g, 2.0 [micro]g or 5.0 [micro]g respectively, the amplified band seen.
c, Occasional gonadotroph/ null cell adenomas will demonstrate clustering of cells, paralleling the perivascular pseudorosette-like formation that can occur on permanent sections.
Thus, p53 null cells are unable to downregulate PLK1 in response to chemotherapy, leading to chemoresistance [25, 26].