From CellBiology

Nuclear Body Protein SP100

    • SP100 was first identified as a nuclear autoimmune antigen and is a constituent of the nuclear body.

SP100 interacts with the ETS1 transcription factor

SP100 protein and Promyelocytic leukaemia (PML) nuclear bodies are known to be the main components of PML-SP100 nuclear bodies (NBs). The disruption of this protein can cause acute promyelocytic leukemia (APL) and invovle in DNA virus infection.

  • SP100 binds and interacts to members of the heterochromatin protein 1 (HP1) families of non-histone chromosomal proteins
  • a naturally occurring splice variant of SP100 (SP100-HMG), is a member of the high mobility group-1 (HMG-1) protein family and may thus possess DNA-binding potential.
  • NB-associated SP100 protein complexes with members of the HP1 family of non-histone chromosomal proteins, both in vitro and in vivo, and that these complexes are seen to concentrate in the


  • SP100 NBs may affect chromatin structure by the finding of a SP100 splice variant, SP100-HMG, characterized by the presence of potential DNA-binding domains, the HMG boxes.
  • involvement of NB components in the control or maintenance of chromatin or heterochromatin architecture.
  • transcription-regulatory proteins and play a role in autoimmunity, oncogenesis and virus-host interaction.


The Sp100 and promyelocytic leukemia proteins (PML) are constituents of nuclear domains that make nuclear dots (NDs) or known as PML bodies. SP100 protein and PML are covalently modified by the small ubiquitin-related protein SUMO-1. The modification requires nuclear localisation signal (NLS) and involve some lysine residue.

As a protein family, Sp100 has subfamilies such as Sp110, Sp140/LYSp100 and the autoimmune regulator protein (AIRE)that share an N-terminal HSR (homogeneously staining region) domain. [1]

Sp100 proteins have different splice variant forms:

  • Sp100 A, contains 480 amino acids - the most abundant form
  • Sp100 HMG, the large variant, contain extra functional domains such as a SAND domain and a HMG box.

These splice variants are the one that will be modified by SUMO-1.

The functional sites of the Sp100 protein were located only in the surface of exposed regions.


1984 Discovered as targets of autoantibodies in patients suffering from the autoimmune disease primary biliary cirrhosis.

1990 After the discovery, the protein was named SP100 (speckled protein of 100 kDa) after forming a 'speckle' shape in the nucleus by using sera from the patients.

1996 Identification of novel nuclear domain as a dot pattern.

1998 novel protein motif, the HSR domain, was discovered , within this ND targeting/dimerisation domain.



Nucleus is one of the main components and only present in eukaryotic cell. It conducts DNA trascription to mRNA and mRNA need to be exported to cytoplasma to undergo translation to protein.

Nucleus has a double layer membranes that is connected to Endoplasmic Reticulum continuously. Cytoskeleton is also very crucial in order to hold the shape and structure of nucleus. The surface contains nuclear pores whereby passive transport of small ions and active transport of macromolecules can pass through.

Nuclear bodies contain specific compartments such as Cajal Bodies and PML bodies which fuctioning as modificator of small proteins and regulate the whole body's function respectively.


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Other examples are cell signalling, cell reproduction such as mitosis and meiosis.

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Two major types of Confocal microscope generate its signal are by:

  • Laser Systems for Confocal Microscopy

The source is from fluorophores whereby the biological molecules reach the excited state and emit ultraviolet or visible light photons and captures them to produce the image of specific structural components of the cells. The technique is advanced by the use of interference filters as well as Spectral Bleed-Through Artifacts (crossover or crosstalk) that is used for broad bandwidths and asymmetrical spectral profiles fluorophores. Laser Systems stimulates and amplifies the molecules with excess energy to emit light. It is the most common light source for scanning confocal fluorescence microscopy.

  • Non-Coherent (non-laser) Light Sources for Confocal Microscopy

This technique use traditional tungsten-halogen source and a short-arc lamp for fluorescence excitation.

  1. Möller, A., Sirma, H., Hofmann, T., Staege, H., Gresko, E., Lüdi, K., et al. (2003). Sp100 is important for the stimulatory effect of homeodomain-interacting protein kinase-2 on p53-dependent gene expression. Oncogene, 22(54), 8731-8737.